My theory for Dante's age is something like this, but again, it's only a theory.
DMC3-18-20
DMC1-25-28
Anime- a year or two older than he was in DMC1, though mostly I figure between 26-28
DMC4-mid 30's
DMC2-early to mid 40's
All of this being said (I've gone over my own theories a lot on this) I'm open to pretty much any theory. My only certainty is that Nero is of the Sparda bloodline, one way or another.
I just wanted to respond to this, as I'm certain I have the correct ages.
DMC1: Dante is 28. At the beginning of the game, Trish literally says Dante ''lost a mother and brother to evil twenty years ago.'' Since Dante was eight when Eva was killed, that makes him 28.
DMC2: Dante's age is unknown. All that is known is that DMC2 is set after the events of DMC4. However, Capcom also doesn't like to admit that DMC2 is a DMC game at all, so I think they don't care about the DMC2 timeline.
DMC3: Dante is 19. This is known: as far as I know, the developer specifically said he was 19.
DMC4: Dante is about 30. Capcom officially stated that in DMC4, Dante is '
around ten years older than in DMC3'. So with a margin of error, that would make him 28 to 33. If he were 34 or older, that would make him ''about fifteen years older than in DMC3'', but they specifically said
ten, so that's 33 at the most. This makes sense to me, because Dante always looked like he was 30 to me.
Nero being Vergil's son always seemed idiotic to me, because that would mean Vergil got Nero when he was like 11 (DMC4: Vergil would be 30, Nero is 19. 30 - 19 = 11). Let's say he were 33 (highest estimate) - that would still mean he had Nero when he was 14. Not very likely, especially when you consider Vergil wanted nothing to do with humans. Even more so since he was always looking for 'power'. If he had Nero, that means he knew he would have a 'weakling' as a son. He'd never want that. If anything, Vergil would have a kid with a demon. Well, if there are any attractive female demons, that is.