We already have this. We've had this since the beginning. However, I doubt we need to make this more "older kid friendly"
Mostly because, we who are older are probably going to leave soon anyway to make more time for more important things, such as collage, jobs, and possibly dating. Why should we shape this forum the way we want if we're only going to stay for three or so more years? We aren't the future of this forum, the younger members are, and if we chase them away by making this place less family friendly, then it truly will die.
We already have a good thing, why not keep it? Yes, this forum has issues, but we can't have the forums grow up with us. After a while we'll have to face reality, we're too old, we have to move on. These days haven't come yet, but they're fast approaching.
We live in a proper community. Believe me, being homeschooled doesn't cut you off from the world. We know that it's like, and you know what? We already have it! Age restricting won't do us any good.
The opportunity could go both ways. Before stating a plan, check every possibility. Maybe this will help the forums, maybe this will kill it.
Truth be known, I know what you mean by this. However, the forums don't require radical change to achieve this. All that's truly necessary is to be here. To talk to other people, role play if you like, and enjoy your friendships here. That's all communities need to grow stronger. Time, conversation, and relationships.
We can still have relationships with kids who are younger then us, we can enjoy their company, and teach them in a way. Not only would we be teaching them, but they teach us also.