Children and the internet...

At what age did you/ or do you plan to allow your children to be unsuprvised on the internet? I have an almost 17 yr old step-son who has a computer in his room. I do keep a very close eye on what websites he visits-he does not know I know every move he makes online. (I have signed up for a website that emails me every 24 hrs with the websites he visits)....and I also check his temp. internet files when he isnt home. So far--has hasnt had any problems. He has been very responsible in the last 6 months since we allowed him to move his computer to his room. I guess we gotta let go at some point.....so what about the kids in your house?