As soon as protagonist starts to "normalize" himself, and fits the mainstream depiction of suburban preteens, there is nothing left but awkwardly adult children's movie. It will not be comprehended by kids it's meant to entertain, nor it holds any intrigue for those expecting meaningful look at generational gaps.
This is a really stupid movie. Like, really fucking stupid. Seriously, stay away from this movie. Robin Williams plays a literal man child. Literally, a child whose body grows at an accelerated rate, so he looks like a 40 year old at 10.