I have been seeing my girlfriend for four month now. I think I loved her at first because I was crazy about her and it was the first time I felt this way about anyone, I'm not sure if I do love her any more but obviosly I still wouldn't be with her if I didn't love her I think. I am sure though that if I was to finish with her I would miss her a lot! We have not yet had sex, I am not using her for sex and I would not dump her once I have had sex with her, and if I was using her for sex I'm sure that I would have finished with her by now. But now I feel as though I am not as interested in our relationship as I first was. I am 19 years old and she is nearly 17 and I am a lot mature than her. Sometimes I feel as though we get really close then I feel as though were far apart I think it also gets boring. Also I think she maybe too good for me and I am just waiting for her to realise this. But overall I really don't know what to think about our relationship and I really don't know what to do. Should I be feeling the way I do? What shoul I do?

For starters, you don't have to love someone to be with him/her. I'm only a few years older than you, and love doesn't show up in every relationship you have with a person. (If only it did.. )
That being said you should treat your relationship as what it is-don't force love onto it-dont make it serious if you don't think it can be serious. If you like the girl and she likes you, it should be enough to maintain a healthy fun relationship with her..
4 months isn't a very long time.. No strings attatched/fun relationships can last for longer or shorter time.. What you need to ask yourself if you like her enough to want to be in any form of relationship with her.. If not then let her know how you feel and let her down easy.. dont string her along.

I can understand how the age gap can make a difference. Girls at 17 are nothing like girls at 19.. I'm 22 and my ex was 19, I treated her like I would a woman, and I expected things of her that I would expect of a woman. But she was still a child.. This can get in the way of a relationship but you have to balance the pros and cons and see if it can be tolerated.
To be honest though, these young relationships(if they end up being long and both go into their 20's), the guy usually gets comfortable in them and the girl wants to see what else is out there.. (this might sound very specific, obviously the opposite thing may happen-but I've found from experience, and reading these forums that its usually the girl that will get confused.. as once guys have sank into a relationship its very hard for them to want out.. )

Anyway, I'm overexpanding.
Decide whether you like her or not :]

Be honest with yourself, and be honest with her. There is no shame in having your feelings for someone change. It's a darn shame if you don't tell them though. Don't string someone on, let her know how you feel, so she can move beyond this. If the shoe was on the other foot, would you want her to tell you? Just do the right thing, and let her go easy as possible, no games.