Well damdash, this is not official info, but it's a conclusion I have come to...
What I think, since Dante's awakening was the "birth" of his demon form, I consider this undeveloped Dt to be an infant. (I know it's retarded, but hey it's my theory!)
Vergil too for that matter, his DT is probably no more than 1-2 years older than Dante's if even that long. Something about their Dts in dmc3 just say kitten or baby, whatever you want to call it, they're infant demons.
Does anyone else think this or am I on crack?