I disagree with tattoomaster completely.
You've probably read my story somewhere else. But I was 16 when I met my partner, and he was 21. Too add to this story, and probably make it sound worse- I actually met him on the internet.
My parents weren't very happy about the idea, but they agreed for him to meet me, and we just fell in love there and then.
My best friend, was also in the same situation as me- 16, met a 22 year old guy on the internet. Her parents were completely against, didn't want her meeting him ever, or even talking to him.
So of course, guess who was the one sneaking around, meeting up in hotel rooms and all dangerous things like that- her, obviously.
Okay, the age gap sounds really bad now. But think about your parents, or family friends. I bet they have the same age gaps or more. That's the way I always looked at it.
And I was hugely mature, and my partner is quite young for his age. So we seem to meet perfectly.
Whatever you do, don't push parents or friends out of it, listen to their opinions, whether you believe them or not. Because it's much more likely to end in tears if you sneak around.
If you really like each other, and wait for any kind of sexual relationship until she's at least 16 and you're both ready, then I see no problem with it.