It's normal for a young woman to start thinking about a family and having kids of their own someday. However, you are only 17 - you still have your whole life ahead of you yet. One of the best pieces of advice I have ever gotten was from my grandma (who had her first kid AND marriage at 16): "'Wait 'til you're 25 to start having kids. That's a good age. Enough time to get the wildness out of your system, to get the things done that you'd wonder 'what if' about - what if I hadn't had my kid, could I have done this... it's enough time to figure yourself out, to learn to take care of yourself. You can't raise a kid when you don't even know how to take care of yourself. 25 is a good age because you're old enough to handle the stress of a life depending completely on you, but you're not so old that you'll be completely gray when they get their diplomas. You'll be young enough to chase your grandkids around and not ache.'"
We had this talk many times because I would always let my romantic heart run wild and I'd tell her how I was destined to marry the guy I'd just begun to date a few months prior. She'd always tell me to slow down and enjoy my life. She said she never regretted having her kids but if she could change one thing she would have waited longer to have them.
I guess my advice is really hers: it's fine to think on it and dream of it, but don't be in a huge hurry to end the exploration of your life and yourself to start a family. Don't get stuck wondering "what if".