Help? Having social issues?

Hi. I'm 15 and have a girlfriend who's 18. We have been dating for around 8-9 months. Now, i'm not one to be chronically depressed or anything, but every once in a while I get upset and think that i'm just a kid compared to her and that we aren't equals because of rights she has that I don't. Rights like being able to vote, drive, be out past curfew and make her own decisions, etc. Also, I skipped a grade and nearly everybody I consider to be my peers are driving, while I cannot yet. My girlfriend (who is one year ahead of me in school, because she got held back over missing too many days of school in the 6th grade from mono) has been driving for 2 1/2 years, while i have another 4 months before i can even get my permit. She doesn't really care about voting and counts my opinion on the same level as her mother's as far as her decisions go, but I still feel slighted in some way. I don't think of her badly for not wanting to, but I sometimes feel like she has rights she takes for granted that I would greatly appreciate. Then, when I get upset like that, I try to think of something that I have that she cannot get yet to feel like we are equal, because while she can do things i can't, I can say the same. There isn't anything I can really think of, however, and thinking about that makes me even more sad. I've always looked at adults differently than my peers (no matter if they are or are not in a position of authority over me) while I can't really relate to the people my age because most of them aren't exactly people you'd consider the sharpest pencil in the box, if you get what i'm saying. I consider my peers the people in my grade or in a grade or two ahead, so when they start getting access to freedoms I can't yet, I feel like they are above me in some way. Everyone I talk to about this says "just wait, you'll have your turn eventually" but it doesn't exactly level the playing field. After all, the only thing that separates the student from the professor is who was born and went to school first! A lot of people say that I am wise beyond my years, but I feel like somewhat of a savant in that while I do appreciate life and know/think about things most people my age have no idea about, i'm just a "whiz kid" so to speak. A "kid" dating an adult. The situation is extremely difficult to deal with because one half of me is accepting her on my level as an intelligent peer, and the other half is wanting to put distance between us because of the age difference. Fortunately, for both our sakes, the second half rarely rears its head, and she always tries to help me, but I still feel bad. Anybody have any advice on how to cope with this?