Puppy hates walking

Question
Hi,  I have a 6 month old chocolate labrador who hates walking.  He has never been very keen, but recently seems to want to go out less and less.  He acts like a puppy sometimes but most of the time is more like an old dog.  Just raises his head when we come in but doesn't bother to get up to greet us.  The only time he is really excited is when he is eating or there are other dogs around.  I take him to puppy classes every week, where he is the best behaved dog you could imagine!  Please help.

Answer
Have you talked to the vet?  He should be in about now for rabies and neutering.  What are you feeding?  Most of his calories now should be coming from a commercial dry dog chow.  Too much of anything else, and he maybe lacking in something.  An early switch to adult chow helps develop stronger joints.