As long as he is under 6' tall. The bunk beds didnt seem to be that bad i had five year old twins in top bunk and a tall thirteen year old in bottom. They had no complaints.
My son who is 6'2" can sleep on the sleeper sofa or sleeper chair. The last time he did a bunk bed at WDW was at the AKL when he was 10 and he just fit.