Hey, I'm turning 20 in two weeks and I've been with my boyfriend for almost 4 years now. I'm a fairly conservative person when it comes to relationships and stuff so I get what you mean about not wanting to just date for the sake of it...
Still, you have a lot of time.. I mean this age is a weird age as it is trying to find yourself.. and I'm sure a lot of the guys you said you could see being in a serious relationship with are going through the same thing.
So just don't think about it so much, I say, just hang out with them and let yourself like them, don't think so much about marriage. Marriage is a whole different thing, ya gotta be in a relationship first :p
I can say that at almost 4 years now, my guy and I feel like we belong together and marriage is inevitable, but there's a lot of other things that has to be done first like finishing college, getting a career going, etc.. but its the security of knowing that we feel that way about each other that makes marriage something worth waiting for, and yeah I love him to death but you'd be kidding if you think we'd go into marriage without some type of counseling :dizzy: I'm not perfect, he's not perfect and we're certainly not ready for marriage yet; but when we are, we'll prepare for it.
Chances are, when you meet your guy too, neither of you will be perfectly prepared to get married, so don't base it all off of that. Marriage takes work - scratch that... relationships take work! It isn't perfect but finding someone who loves you and is willing to work at a relationship is what's important.. someone you could eventually grow with into marriage.

I also think love finds you when you least expect it, so just enjoy life and whatever happens, happens. :hug: