Millen is 24, is a product of US college, where he did pretty well, and now seems to be giving full attnetion to tennis (I think he's based at the Uni of Bath, at the moment).
I didn't see him as a junior (don't know why). But I've seen him play a few times in the last few years and there's a lot to like there. Just in my rating, I wouldn't put him in Jake's category, who's always been a fave, but I rate him more than Patrick Brady (although Brady is very young and, as Jaggy rightly says, maybe I don't really appreciate his qualities) or Emile Hudd, who I never really rated as a youngster (maybe wrongly)