I'm afraid I can't find sources, but I can tell you my views and why I think they make sense. I can also tell you what we know and what we don't know.
DMC1: Dante is 28 (this we know). Trish said Dante lost his family 20 years ago. Manga said he was 8, so that makes him 28.
DMC2: age unknown
DMC4: I remember Itsuno saying years ago that Dante was ''around ten years older in DMC4 than he was in DMC3''. Considering Dante was said to be 19 in DMC3, that would mean he's about 30 in DMC4. But it never came up again, so I wouldn't put stock into it. AND if Vergil is Nero's father, it wouldn't make sense for Dante to be 30 in DMC4... because Nero is said to be the same age as DMC3 Dante. So... 30 - 19 = 11. Vergil conceived Nero when he was 11? Naah.
In DMC3, Vergil said that it had been a year since him and Dante met, so that could mean Vergil conceived Nero when he was 18. The DMC4 SE teaser shows Vergil holding *something* under his cloak. So, 18 + 19 = 37. Dante is probably 37 in DMC4. As for plotholes, I can think of *one*: Dante had not met Vergil in DMC1, but in DMC3 he fought him on the Temen-Ni-Gru.