Well, he has been waiting all day to play, so it is not surprising that he is ready to go and go and go when you get home.
Have you tried running with him? Biking with him? Frisbee? Obedience training? These are smart, energetic dogs and need a job to do. In addition, yours is still a pup.
As for the dog park, he might be overwhelmed by so many dogs, that, let's face it, are not always balanced. You never know what kids of dogs you run into over there.
A great game is find the treat. Hide a treat or ten somewhere in the house, and encourage him to find all of them.
Perhaps a doggy day care might be in order. He has fun all day, and you get a tired dog when it is time to go home.