You're interested, but don't have a crush? Frankly, this makes no sense to me. I don't understand what you feel. Plus, the fact, that you're old enough to be at university, but have never felt anything beyond, "Huh, she looks good" suggests to me that you might lean toward asexuality.
Not to be all I was so smart and mature for my age etc. but high-school isn't always the best place to meet guys/girls/whatever especially if you have very different interests and operate on a different intellectual level. You don't even need to be Holden Caulfield and hate the world - you can even still have friends and have fun and not be a stereotypical aloof nerd without really ever feeling romantic attraction for anyone. While I definitely liked people outside of school, I can't say I ever was romantically interested in/had a crush on/liked someone my age as a high-schooler.
In conclusion, maybe he's not asexual and just didn't really connect with people in high-school?