Well,... I do remember feeling uncomfortable when at 19, I was dating a 16 year old girl. I was actually worried that I was breaking some law, unaware that it was actually legal (at least where I was living).

In any case, 11 years later we are still together, so it can work. If your girlfriend is 17, you just have to accept that it won't always be an easy ride for you, since she will learn the ropes through you. I guess going out with a more mature woman is more peaceful, since she will have got more maturity at some other guy's expense ;-)