who you let your kids talk on a online chat room at the age us 12or13??

I have a 12 year old son, and yes I let him chat on line with his friends, but I am always checking to see who he is talking to and he never has his door shut so that I can pop my head in and check on him occasionally. I do limit his internet usage to just a couple of hours on the weekends or rainy days when we are at home. Most of his friends he IM's with are his school buddies to begin with, and I have full access to his email account. He enjoyes it and is happy and I can rest stress free that I am doing what I need to to keep him safe.