I actually have some experience in this. I skipped a grade which made me younger than the kids in my class. This was fine as a small child but I was also a nightmare teenager. Some of it was just because it was fun to raise hell but mostly I had a lot to prove. To my parents great concern at the time I actually took a year off to work before going to college and I really needed that year to just calm down and mature. This did not make me a model college student in terms of abtencence but it did help me to become aware that being and adult was not about smoking my bodyweight in grass.
Perhaps look at some stimulating co curricular activities or look at a school which has more to offer a gifted child. Whatever you do be mindful of the adolescent years and think about how you are going to manage a child who will feel the need to fit in with kids a year older
