The average lifespan in 0 AD was something ridiculous like 35 because of infant mortality. Let's say that I'm a healthy person who can afford the best medical care Rome had to offer. Could I come close to living as long as people do today? Would getting past 90 even be possible?
The average life expectancy well into the Victorian period was roughly in the 20s because of the extremely high infant and early life death rates, assuming you could get over that in ancient Rome the average life expectancy for anyone over that main gap was around 70-75. If you assume you had a healthy lifestyle is not impossible to imagine going into the 80s.
The past 90 thing is really situational but it happened, but would require a mix of healthy living and basically luck to avoid accidents or diseases. The book Macrobii is dedicated to long lived people in Roman Empire period, but is admittedly probably inaccurate. The Roman censuses also record people living people living to be up to 130 or more which also admittedly seems inaccurate due to the fact that people may of not had exact idea of birth date depending on their birth conditions.
One could compare the Diadochi, the heirs of Alexander the Great, that is two and a half centuries before, but not that far away. They were upper class Macedonian warriors who had a decently healthy regime of training (but it seems they loved to drink, a lot).
Perdiccas was assassinated 320 or 321 BCE, so I will disregard him.
Craterus was killed in battle 321 BC, at the age of 51, so I will disregard him.
Antipater died of what was described as old age in 319 BCE, at the age of 80.
Ptolemy died 283 BCE at the age of 84.
Lysimachus died in battle 281 BCE at the age of 79.
Antigonus died in battle 301 BCE at the age of 80.
Seleucus was assassinated in 281 BCE at the age of 61.
As you see, these men were healthy enough to lead troops at advanced ages and several of them survived into their 80s.
Adding some emperors to vonadler's list you can see some decent ages there too:
Augustus - 75 years.
Vespasianus - 69 years.
Nerva - 67 years.
Antoninus Pius - 74 years.
They are all well short of the 90 you're requesting, but they would have had the best medical care available being emperors and they by no means lived a passive life.
Does it have to be a man though? Asking for a politician kind of automatically makes the question aimed towards the male population, but if I can take some liberties and turn your eyes towards a woman (who definately was a politician, albeit inofficially), I'd suggest you take a closer look at Livia. She was the wife of Augustus, the mother of Tiberius and grandmother of Claudius and thus the most powerful woman in Roman history.^1 She also lived to be the oldest Roman I can think of, with her death at 87 years of age. That still doesn't break your limit of 90, but it's close enough to suggest that it was possible - given the right person.
[1] I suspect I'm going to have to source that claim, so although it may still be a tad subjective:
No Roman woman ever wielded such power and influence as Livia. (Donald R. Dudley (1968), The World of Tacitus)
There's an excellent article by Bruce W. Frier called Roman Demography which may be of interest to you. It was published in a book: Life, Death, and Entertainment in the Roman Empire, edited by David Stone Potter and D. J. Mattingly (Page 85 onwards).
He discusses life expectancy in the Roman Empire. Frier explains that determining a life expectancy is very difficult as we have few surviving records indicating age etc. He gives a life expectancy at birth of 21 years. If you were lucky enough to make it to 10 years of age you could expect another 35 years of life (so life expectancy of 45 years). He further adds that people aged 65 and over made up an estimated 3% of the population of Roman Egypt.
Hope that helps somewhat!
Pliny the Elder, writing in AD 77–79, noted several incidences of long life in his book Natural History:
Not only the differences of climate, but the multitude of instances named, and the peculiar destiny attached to each of us from the moment of his birth,1 tend to render one very uncertain in forming any general conclusion respecting the length and duration of human life. Hesiod, who was the first to make mention of this subject, while he states many circumstances about the age of man, which appear to me to be fabulous, gives to the crow nine times the ordinary duration of our life, to the stag four times the length of that of the crow, to the raven three times the length of that of the stag, besides other particulars with reference to the phœnix and the Nymphs of a still more fabulous nature. The poet Anacreon gives2 one hundred and fifty years to Arganthonius,3 the king of the Tartessii; ten more to Cinaras,4 the king of Cyprus, and two hundred to Ægimius .5 Theopompus gives one hundred and fifty-three years to Epimenides of Cnossus; according to Hellenicus, some of the nation of the Epii, in Ætolia, have completed their two hundredth year; and his account is confirmed by Damastes, who relates that Pictoreus, one of this nation, who was remarkable for his size and strength, lived even to his three hundredth year. Ephorus says that some kings of Arcadia have lived three hundred years; Alexander Cornelius, that there was one Dandon, in Illyricum, who lived five hundred years. Xenophon, in his Periplus, gives to a king of the island of the Lutmii six hundred years, and, as though in that instance he had lied too sparingly, to his son eight hundred.6 All these statements, however, have originated in a want of acquaintance with the accurate measurement of time. For some nations reckon the summer as one year, and the winter as another; others again, consider each of the four seasons a year; the Arcadians, for instance, whose years were of three months each. Others, such as the Egyptians, calculate by the moon, and hence it is that some individuals among them are said to have lived as many as one thousand years. Let us proceed, however, to what is admitted to be true. It is pretty nearly certain, that Arganthonius of Gades7 reigned eighty years, and he is supposed to have commenced his reign when he was forty. Masinissa, beyond a doubt, reigned sixty years,8 and Gorgias, the Sicilian, lived one hundred and unwittingly the father of Adonis, by his own daughter Myrrha (or Smyrna), in consequence of the anger of Venus or Aphrodite. He was said to have founded the city of Cinyra in Cyprus. eight.9 Quintus Fabius Maximus was an augur for sixty- three years.10 M. Perperna, and more recently, L. Volusius Saturninus, survived all those whose suffrages each had solicited on the occasion of his consulship;11 Perperna lived ninety-eight years, and left after him only seven of those whose names, when censor, he had enrolled. Connected with this fact, it also suggests itself, and deserves to be remarked, that it has happened only once, that five successive years have ever passed without the death of a senator taking place; this was the case from the occasion on which the censors Flaccus and Albinus performed the lustration, in the year of the City 579, until the time of the succeeding censors.12. M. Valerius Corvinus completed one hundred years, forty-six of which intervened between his first and sixth consulship.13 He occupied the curule chair twenty-one times,14 a thing that was never the case with any one besides. The pontiff Metellus also attained the same age.15
Among women also, Livia, the wife of Rutilius, exceeded her ninety-sixth year; during the reign of Claudius, Statilia, a member of a noble family, died at the age of ninety-nine; Terentia, the wife of Cicero, lived one hundred and three years, and Clodia, the wife of Ofilius, one hundred and fifteen; she had fifteen children.16
Lucceia, an actress in the mimes, performed on the stage when one hundred years old, and Galeria Copiola returned to the stage, to perform in the interludes,17 at the votive games which were celebrated for the health of the deified Augustus, in the consulship of C. Poppæus and Q. Sulpicius.18 She had made her first appearance when eight years of age, just ninety-one years before that time, when M. Pomponius was ædile of the people, in the consulship of C. Marius and Cn. Carbo.19 When Pompeius Magnus dedicated his great theatre, he brought her upon the stage, as being quite a wonder, considering her old age. Asconius Pedianus informs us, that Sammula also lived one hundred and ten years. I consider it less wonderful that Stephanio, who was the first to dance on the stage in comedy descriptive of Roman manners, should have20 danced at the two secular games, those celebrated by the deified Augustus, and by Claudius Cæsar, in his fourth consulship, considering that the interval that elapsed between them was no more than sixty-three years;21 indeed, he lived a considerable time after the last period. We are informed by Mutianus, that, on the peak of Mount Tmolus, which is called Tempsis, the people live one hundred and fifty years, and that T. Fullonius, of Bononia, was set down as of the same age, in the registration which took place under the censorship of Claudius Cæsar; and this appeared to be confirmed by comparing the present with former registrations, as well as many other proofs that he had been alive at certain periods—for that prince greatly interested himself in ascertaining the exact truth of the matter.
Seneca the elder(54 BC- 39AD) comes to mind. A roman aristocrat and rethorican, actually lived to be 93 years old.