Well, I looked up the interview, thanks to Sparda(tm), and Kobiyashi's exact words were "Lady is about ten years older". It's a rounded off generalization, not a solid "lady IS Ten years older". Thusly, anyone saying "it's ten years later, no less or more" is missing that key generalization. Ergo, it's give or take a year or two, not "it's exactly ten years". Since the first solid statement of "this game takes place this long after this one was in fact "DMc3 is ten years before DMC1, which is twenty years after EVA was killed", that places DMC4 as about a year or two after DMC1.
Ergo, Dante and Lady are in their 30s in DMC4. IN fact, it was also said that Dante and Nero are ten years apart, and Nero is in his early 20s. So unless it was suddenly retconned that they're less than ten years apart, and making Dante even younger when Eva was murder by proxy...there's no way Dante is less than 30 in DMC4.
As to the anime, it keep making itself ambiguous to the exact time frame after DMC1 it happens, only that it's before DMC4. Yes, Dante's in his DMC1 outfit. However, he has also traded up Enzo for Morrison as his agent, and dialogue insinuates that it has been a good while since DMC1, plus the fact of Trish's rant at Dante that "I've been telling you for years to lay off the pizza." I also keep hearing that DMC4 is actually a year after the anime from several other people, so since neither the show itself, the show materials, nor the producers give an exact dating...all we can say is "it's between DMC 1 and 4", within about a two year time span supplied with the less than four year gap between the two games given by interviews.