DMC1 states within itself that Eva was murdered 20 years prior, and Dante was 8 at that time, so he's 28 in DMC1. DMC4 takes place 10 years after DMC3 as stated by game director Kobiyashi, and Dante was established as 19 in DMC3. Also stated in that same comment is that Nero in DMC4 is the same age Dante was in DMC3, thus, Nero is officially 19 in DMC4, and Dante is 29, so DMC4 is about a year after DMC1 with the anime happening in that year time span. The omnly game we have no stated time frame for is DMC2, and I dont' believe NT has said one for Dante's age yet in DmC, but it's safe to saye within 18 to 23 likely.