I suggest playing online games and meeting people that way.
Or log onto PlayStation Home by clicking on the "house" icon on your XMB, create an avatar and explore. There are over a hundred games in Home and you might find something that you will like.
And if you do join Home (it's free), come visit and share on the official forum PlayStation®Home.
Good luck and have fun.
21 years old on PSN during random hours and adds would be appreciated! PSN: tasogare--
As well as what Conrad has suggested you should also take a look at this Thread, it is specifically designed for people looking for friends to play/game/talk with...