Hey there,
This really has to be your decision to make - none of us here can tell you what's the right or wrong thing to do. From your post alone, I can tell you're really mature for your age and I believe you can make the right choice. Age honestly doesn't matter that much and it's only a three year difference tbh.
If you think going into this relationship is a good idea, then do it. If not, then don't. Regardless, relationships rarely last forever at this age so it's not like you can't ever get out of a bad decision if being with him does turn out to be one.
Hope this helped somewhat (sorry it was quite inconclusive but I really think this should be your own decision!),
and feel free to
PM me if you ever need to talk,
Kyra xx