What we call pedophilia was clearly widespread in the Roman world. Even if we can dismiss some of the more sensational stories recorded by our sources as hostile gossip (one thinks of the Emperor Tiberius and his "minnows" (slave boys trained to...nibble him) or of Nero castrating and "marrying" a slave boy), the sheer abundance of such references makes it clear that sexual abuse of minors was a fact of Roman life. To our eyes, of course, all such abuse is horrifying. For the Romans, however, it was only problematic (morally or legally) if the abused child was free - and especially if he or she belonged to a good family. Slaves, on the other hand, were property; and despite the gradual appearance of laws intended to protect them from the worst barbarities, their bodies were always subject to their masters' whims.

Although abuse of minors occurred at all levels of society (elite parents, for example, were always careful to inquire into the character of their sons' tutors), it was always most prevalent between masters and slaves. Auctioneers could count on receiving excellent prices for handsome slave boys; some, we are told, took pains to make adolescents look even younger, knowing that this would make them more marketable. References to the abuses young slaves suffered could be multiplied almost at will. To take a fairly well-known one from Seneca:

"I shall not mention the troops of luckless boys who must put up with other shameful treatment after [a lavish] banquet is over. I shall not mention the troops of [slave] catamites, rated according to nation and color, who must all have the same smooth skin, and the same amount of youthful down on their cheeks..." (Ep. 95.24)

Tellingly, Seneca's diatribe is concerned with the moral weaknesses revealed by the custom of keeping slave boys, not with the welfare of the slaves themselves. Despite the protestations of some philosophers, virtually all Romans simply placed slaves in a different moral category, and viewed all the horrors they suffered as nothing more or less than a regrettable consequence of their condition. At most, they might describe love of boys as an unsavory import from the Greek world, contrary to Roman tradition and the canons of self-control.

Over the course of the early imperial era, a series of emperors passed laws designed to limit the abuse of slaves. Claudius declared the sick slaves abandoned by their masters would be freed if they recovered. Domitian forbade the castration of slave boys. Hadrian repeated the ban on castration, and barred masters from selling slaves to brothels or gladiatorial schools. These laws, however, were difficult to enforce. And none of them said anything about sexual abuse of young slaves.

At least some Early Christians seem to have been more staunchly opposed to the abuse of slave children than most polytheists. The second-century Epistle of Barnabas, for example, elaborates the commandment "Thou shalt not commit adultery" with the comment "thou shalt not corrupt boys" (19:4). I'll leave extended discussion of the patristic texts, however, to someone who knows them better. The answer to your question, in any case, is clear: before the Christianization of the Empire, the legality and morality of what we call pedophilia depended on the status of the abused child. A free boy or girl was protected by law and custom. A slave boy or girl, tragically, was not.

In addition to the previous comment, the definition of pedophilia has basically been a moving goalpost from culture to culture and era to era.

If you look at the basic statistics for the first marriage of women of noble birth, they tended to be half the age if their husband. Young women (who I would argue were still children) could be married to a man 30+ when she was 14-18. Peasants/plebeians were more likely to marry much closer in age and later for women. In other words, poor women typically didn't marry until late adolescence or early 20s, while rich women might be expected to marry much younger to establish political/finacial/familial ties.

Men could, and certainly were, involved with boys much younger than themselves. For the Romans, it came down to who was in a position of power, age, and who was expected to do what in the sexual encounter. For them, the act of penetration was of utmost importance - someone in a position of power was not supposed to be penetrated lest they relinquish their "manliness" over their partner (willing or not).

There did not seem to be encouragement on the sexual abuse, rape, or molestation of children before puberty. However, as mentioned above, the abuse of slaves undoubtedly did spread to child slaves, but it was frowned upon. But once a child slave reached puberty there is a very good chance they were fair game to their master's desires.

The condemnation of such disgusting behavior also seems to have followed specific emperors - like Tiberius or Nero. They did not go down well in history, then or now, and they are subject to the question if they actually did those terrible things.

But you can also go look at the relationship between Hadrian and Antinous (born in 138 and 111 respectively). Faustina the Younger married Marcus Aurelius in 145 AD at age 15. And so on and so forth.

I think that this is an important question and one that is hard to answer. Both ancient Rome and Greece can basically agree that sexually engaging in any way with an eight year old is gross, but they only move that goalpost to puberty/menstruation/early adolescence for the people that might be affected (slaves and young women).

At what age did a Roman stop being a "boy" and become a "man"? "Adulthood" is a nebulous concept. Across history, societies have a nebulous and shifting concepts of this, not always lining up with chronological age, owing more to looks. How did this work for this work for the Romans?

If what we'd considered a boy looked a certain way, were they now regarded as a teen or a man? Or, like now, did the Romans consider you a boy until you hit a particular year of life?