Wow, 16 is sooo old. I'm sure plenty of great mathematicians didn't know what they wanted at 16 either.
25 is pretty young still I think. Thats only 3 years into a PhD, so really I wouldn't expect anyone (except super geniuses) to make many achievements by that age. I'd say 30 between 27 and 30 seems like a pretty solid age, as you've reached a peak with your PhD and you're still young and inquisitive and hopefully humble.