He wasn't a pedophile, at least from what I've read. Pedophilia specifically refers to an attraction to prepubescent children - Epstein was interested in adolescent girls, which would make him a hebephile. If Epstein was going around with an entourage of 10 year old girls it would've been extremely obvious, and he would've been arrested in about 5 minutes. OTOH it can be legitimately hard to tell the difference between a 14 year old and an 18 year old. People may have heard rumors or had their own suspicions, but they probably weren't sure and that uncertainty made it easy to take the safe route and stay silent...
I haven't followed his case well enough to know the age range for his young friends. But yes, I don't recall that he was grooming ten year olds. But probably 13 year olds, I think.
And yes, it's hard to tell about preteen people. Looking back at old pictures of close friends and myself, the most obvious changes were later, at maybe about 19-20. Mainly a loss of gangliness, I think. Puberty is not uncommon now before ten, so secondary sexual characteristics alone are unreliable indicators.
Way back in the hippie days, when I was about 18-20, I had a few 13-16 year old girlfriends. And I don't recall that they were all that obviously distinguishable by age. But of course, in old pictures, we all look like children.