I agree that if he can stand up and turn around, the kennel should still work for him.
However, if you wanted to try him outside the kennel to see how he does, you could always stick him in a bathroom or some other room with tile floor to see how he does. I think Gunther was about 5 mo when I started letting him stay in the bedroom at night......... ..I had to, he outgrew the largest kennel I have. Luckily, he whines if he has to go so it wasn't an issue.
If you do try the bathroom route, just make sure there is nothing he can get into in there, and give him a nightlight so he's not in the dark.