I think so far as age related stuff goes Second Life is perfect in it's current state really. Adult content is a big part of SL, and trying to make SL g-rated or something, would ruin a lot of good things about it. For both moral and legal reasons there are many 18+ zones, which allows all that adult content to exist without being in every single zone, and imo that's the way it should be.
I don't want adult content to all be removed in some attempt to make SL all g-rated, and I certainly don't want to lose various adult only spaces that mean a lot to me. I'd be devastated if that ever happened, and if minors invaded these places, I'd start to feel a bit creeped out and highly uncomfortable. As for what you mentioned, yes I'm sorry that some minors feel homogenized with much younger minors but the line has to be drawn somewhere, and the most important thing being keeping minors out of adult specific places.
Yes SL is very much adult oriented, this isn't a bad thing though. Some things just simply are heavily adult oriented, and that's a part of what makes them what they are, that isn't inherently bad or anything. Honestly if someone whose under 18 wants to explore everywhere in Second Life, they should probably just focus on other things until they're actually 18+.
There's also much better cyber worlds and or video games for minors to be playing anyways, stuff that isn't so heavily adult centric. Let Second Life remain the heavily adult oriented world it is, and just let minors focus more on less adult oriented media, that's how we can prevent any of these problems in the first place.
Some games, cyber worlds and so on, are built upon centering certain groups, and trying to focus on fully pleasing everyone with it, dillutes and ruins them. Which is why I feel if someone isn't part of a group a game, or online world is centered upon, that they should just find something else. That way no fighting over it, no lawsuits, no hurt feelings, and nobody loses their favorite stuff.
I'm sure there's some groups on SL I would severely dislike if I went out of my way looking for them- and you know what I do? I simply avoid them.
TLDR: Please do not ruin Second Life by dilluting what makes it such an awesome place, just to make it more family friendly.
If you want a G rated online world or game, then you're not looking in the right place.