Oh, I understand how you feel! Try not to worry too much, though, especially about his age. My Bear dog who was a pound rescue was about 5 years old when I found him and according to the rules for adoption I had to have him neutered. It didn't change him or seem to bother him in the least. He really didn't act like he was uncomfortable afterward, either. I think by the time the anesthesia was completely out of his system - he was a bit groggy and wanted to sleep when I picked him up that afternoon - the next morning he was basically comfortable.
Let us know when your little fellow is back home and playing with you again. He'll be okay.