I've always wanted to be 30. I'm 27 now. But it seems like 30 -- not a year more or less -- would be perfect. LOL -- I'm running like crazy now and trying to eat right (somewhat) so I'll look like I'm 30 for a while when I get there.
I might pick younger -- but if I had to go back to being limited to the knowledge I had yesterday -- I would almost kill myself. Knowledge, to me, is far more important than youth.