LIttle Boy all growed up

We went to see Dr Dan today. Alex, after an hour, came to the conclusion, that maybe, he would be willing to work with me.
  Of course we had to find a deal where, he could still be all grown up, in 3 days he is old enough to buy grown up games, and go to grown up movies, but how do I stop him from making the big mistakes.
  I worry about how he will handle the change of being an adult, when inside him there is a little boy who still throws things and he doesn't like it when changes happen.
  It is hard to let him grow, when the behaviors are still the same, but they are changing as he gets older, and he wants to make the grownup decisions. He works at the decisions, and he thinks of the things he can do when noone can tell him what to do.
 Who can give me an idea, and how can I findthe answers needed, so I can let my son grow, and yet not let him fall apart.