Personally I think you are a bit young/inexperienced for 5x5. I know you have been training for a while, as I remember some of your posts from a while back, but 5x5 is very demanding not just on your musculature but on your nervous system.
It's great to see someone of your age with such an interest in training though, and a desire to improve.
Personally I think you should keep your reps higher, do a lot of bodyweight training, run sprints, do gymnastic type drills and that kind of stuff, and just have fun with your training.
It is going to be very hard for you to gain size given your high level of activity and age. While I don't subscribe to the myth that weight training will stop you growing taller, cumulative overtraining from all your activities could.
Just some thoughts.