I would get him the dog instead.. :)
I had my son in the hospital for two weeks due to samonella poisoning thru a little chick. And then after that, we did have a turtle, but we kept it in the tank. We've gone thru many pets, and now we just have two puppies, and fish tank. That's perfect now.
If you do keep it, let him know that if he wants to handle it, then he must do it when you are around to watch, etc. And also to make sure that he washes his hands, etc.
If anything, I would say keep the turtle in the tank.. and not handle it..
It's a tough call, but it was a gift, and well I see no harm in keeping it, as long as there are strict rules on either not handling it, or handling it with an adult, etc.