To DrewfromCA - a 17 y/o girl is typically considerably more emotionally mature than 17 y/o boy. That's a fact. I can, however, see why you may not date a 15 y/o when you were 17, because you were 17 and your friends would tease you. I'd also like to point out that:
1. There's a significant difference between a 15 y/o and 17 y/o. A 17 y/o may be just days away from leaving the house and going to college, yet a 15 y/o has just started high school.
2. Some people mature much faster or slower than others. Perhaps the 20 y/o guy dating a 17 y/o really is extremely immature. Oh well. It's really no reason to insult him. I'm sure that, just as there's many people your age who are very immature compared to you, there's plenty of people your age who would make you look immature. It's all subjective in the end anyways.
3. I'm 17 and my boyfriend will turn 20 in August. We've been dating for two years. Whether or not I end up with him forever and ever is not the measure of whether it "works out" or not. If it doesn't, oh well, I learned so much, about love, life and myself as an individual. I treat our relationship as if it's permanent, but if it ends, I'll take more from the experience than it could ever take from me. I realize I'm lucky and that most young relationships are never as long-lasting or positive as mine is, but who are you to judge someone else that you only know by reading a few posts on the internet?
(Sorry that I went on a bit of a tangent, I found that post pretty offensive and condescending)
Anyways, to the original poster, I have a good solution for you. Two words: chastity belt. Give the key to the parents, and they'll worry a lot less.
Actually, don't suggest that. You'll just freak everyone out.