Is 9 years old too young?

My son Austin has internet in his room....Yes, I'm a crazy mom.  I do have limits, he's only allowed to go to certain sites.  I sit and watch him to make sure he follows the rules.  He's really a trustworthy kid, but I get a little nervous with the internet.  Well, he shocked me the other night.  He told me he could go to youtube and get cheat codes for his pokemon ds game.  I don't want him on youtube at 9 yrs old!  I checked it out and sure enough, there are plenty of cheat codes that would help him out.  There is also plenty of other stuff out there that I don't want my kids to know about yet....especially at 9 yrs old!  My friend told me I was silly and he hears about all that stuff at school.  I feel like he may hear about it, but it doesn't need to be seen or shoved into his face at home.  (and I don't think he's really hearing about "all" of it at school just yet!)  What do think of this?  Should I let my son hop on youtube when I'm not around to search for cheat codes or other kid stuff?