A.-
I wouldn't worry too much about it. It's very simple to take the wheels off. If you can make a mix cake you can take the training wheels off.
My son was about your son's age when I did it for him. He was very excited until he kept crashing then he begged, begged, begged, whined, whined, whined, pleaded, pleaded, pleaded that I put them back on. Mind you, this was after a whopping 10 minutes of them being off. About a 1/2 hour after that he was riding around like a maniac. He had balance issues when starting until he was almost 9 years old. So, if you don't think he's ready don't worry. If you are comfortable, it's really easy to take them off. Just know if he doesn't think he's ready, but you do, it could be a challenge.
I'm sure he'll do just fine.
S.