There's effectively no such thing as vikings outside the Viking Age. The term víkingr was used in Old Norse for people who went off on travels. That occurred more often for peaceful trading not raiding, and was in either case a small part of the population of Scandinavia. 'Vikings' is not a collective term for Scandiavians in general, only travelling Scandinavians of a particular era. The term fell out of use in Scandinavia during the Middle Ages (Scandinavian Middle Ages being the era after the Viking Age, circa 1050-1550), and the word was never used in any other languages until Viking Romanticism started int he 19th century,

Scandinavians went on journeys before and after the Viking Age. It is a somewhat-arbitrarily age defined by an external point of view, namely the period during which raids in Western Europe and Britain in particular were common. Scandinavians traded and raided around the Baltic region before the Viking Age and so did other peoples of the area such as Finns and Wends.

"Norse" is also a later term for pre-Christian Scandinavians who did not identify as "Norse" but as Norwegians, Danes, Swedes, Geats. (and further subdivided into more local groups) The farther back you go the more questionable that grouping gets, too, as it gets less obvious whether (say) the Danes and Swedes have more in common with each other around 300 CE than Danes would with other Germanic groups like the neighboring Angles or Frisians.

It's not so obvious Europeans would be more aware of the Danes; the first recognizable reference to any Scandinavian group is to the Swedes, as Suiones in the book Germania by the Roman historian Tacitus around 100 CE, who describes them as having impressive ships. Danes (as Dani) are mentioned centuries later by the 6th century Gothic historian Jordanes in Getica, which also mentions Swedes, Finns (may refer to Sami in this context) and a bunch of Baltic place and people names.

Anyway, Tacitus indicates that the were Romans in Italy who had some awareness of the peoples of northern Europe in the first century. Archaeological evidence from the north shows there was contact at that time as well, to the extent that around the year 1 there is a division in Scandinavian historic periods into the 'pre-Roman' and 'Roman' Iron Ages, not because Romans were there but because of the influx of Roman influences from coins to silver objects. The Runic Script used by Germanic peoples is believed to have been derived from Old Italic script; also during that era. It's generally believed that Scandinavians fought as mercenaries in the Roman legions at the time, as did other Germanic groups. (again, separating out the Scandinavians here is not necessarily meaningful)

But 4th century Scandinavians were not any more than today's Spain is populated by conquistadors.