My neutered boys are still active, playful, and feisty. They both recovered very quickly, but I had to discourage Max was jumping for two weeks. I also wouldn't let him go on long daily walks during that time. Instead, I carried him and eased him back into it.
Another advantage to having waited until 8 months is that your baby's growth plates in his bones are more likely to have closed. Teddy was a little over 7 months when he was neutered. We haven't had any trouble with marking.
ETA: I see Brit already mentioned the growth plates
