No, and as you get older you'll find that a 3 year age difference is relatively minor. It is only significant at your age, and then primarily because of the events at that stage of life. She'll be heading to uni soon if she hasn't already, with everything that entails: dorm life, no curfews, plentiful alcohol, etc. It's a major switch and people change rather drastically when making it. Most of the couples I knew in high school failed to survive it and, even if the two of you are at the same university, your difference in situations would cause complications (unless your parents are fine with you sleeping over in her dorm room/going to late parties/generally behaving like your typical college freshman...in which case just don't turn into my wife's cousin, who started uni at 16 and failed out at 18, a pregnant alcoholic meth user). It's great that you're friends, just don't let yourself get hurt if and when she makes the switch.
On the other hand, you're going to be starting a real career at the same time that your age group is graduating from high school, giving you a major advantage with the ladies at that point in time