I can definitely relate to that. I was developmentally delayed so I got around to a lot of things later in life than most people; even as an adult I didn't have my first relationship/girlfriend until I was 23, whereas all my peers were dating in high school.
My situation is definitely worst. I'm 28 and never had a girlfriend, while my best friend is 25 and has a four year old son.
Sorry man, I know it sucks.
When I was 20-22 at University and everyone but me was dating 'n' mating, I definitely felt left out and like there was something terribly wrong with me. If you'd asked me when I was 22 I was starting to think I'd never get to date or have sex in my life, it was all starting to feel totally hopeless.
I'm afraid the only advice I can give is to put yourself out there as much as possible and not give up.