I had a guinea pig when I was about 10 and I loved her! I took care of her by myself, she was affectionate and loved to be held.

If he is leaning towards a reptile (like many little boys would!) I think they are not too hard to care for. I know my brothers had a few Iguanas... they were about 15 at the time. As long as you help set up the cage and thermostat, I'm sure he'll do well to care for it everyday with minimal help.

Good luck with finding him a pet