I love my hermann! He's so pretty to look at. He's 2 at the moment and in a 4ft tank, if need be I'll replace it as he gets bigger but I was told that would be big enough for him. He's dead active to so he should keep your son entertained. I can watch him for hours just going about his tortoise business
Hermann tortoises can be surprisingly engaging. Mine will leave a full food bowl of his favorite foods to follow me around the yard and porch while I'm doing things, often to the point where he is underfoot! You can't turn around without him. And he hates being left in his enclosure if you are outside and he can hear you doing things without his assistance.