Star, this isn't about the well monitored teen, or even about the perv who wants to initiate contact with a teen for ilicit purposes. This is about a teen accessing content that is not intended for them, intentionally or accidentally, by circumventing the ratings system or other methods.
I used to play WoW. The vast majority of female toons were played by teenage boys. Their explanation - "if I'm going to look at an @$$ 6 hours a day, I want it to be a girls." Go look at any of the moddable 3d RP game fan sites out there, such as Fallout 3. The number 1 mod groups are typically cheats and god weapons, usually followed by 'nude patches' so again said teenage boy can enjoy the view as they run along.
I wish more parents were like you and only allowed computer use in a 'public' family area. That's hard to enforce now that kids are given laptops and netbooks and are usually spending their online time in their bedrooms. And this has nothing to do with good or bad parenting, it's about knowledgeable parenting. Most parents think nothing of Billy spending 5 hours on his homework on his new laptop upstairs. He can't be doing anything wrong because we've installed web filters! Ask that same parent if their child's laptop has a webcam built in. Most do. And most parents do not know. I've been in coworker's homes where this is the case and I'd hardly consider them bad parents.
Now, on to a potential solution for those that want to continue having pixelated nudity and such. I'm not an expert on viewers so forgive me of some TPV can bypass avatar blocking. Enable a 'reverse' block on two levels. First would be on your avatar. Check a box, and teens see you as a blocked avatar and can't message you or enter into any local/group chat with you. You won't see their text, they can't see yours. I would think that logically this would be on by default so the choice to unblock is in the hands of the RL'er.
Next, for those that sell mature content that don't wish their content to be viewable by minors, a checkbox that will block teens from viewing anything that is owned by you. Perhaps make this an additional perm that can't be restricted by the creator - as the creator you can make it blocked so they can't see it in your stores, but once it's in the hands of a customer they can choose to do as they wish. That passes the liability onto the new owner. I also think this should be enabled by default, especially on existing content, or have the avi level ownership block override it either way.
This would allow mature sims next to g sims and circumvent the need to come up with a solution for the cammers, something that LL has admited they don't think can happen.