There's more to it than that.
When I signed up to SL it was perfectly clear: 18+ only, always, end of story.
LL really confused things by allowing people in child avatars in the first place - which is the literal definition of "ageplayer" if there ever was one.
LL further confused things by allowing the child avatars unfettered access to "Mature" or "Adult-Only" rated areas.
When LL inflicted Zindra on us, they had the chance to fix that problem, and Jack Linden blew it under pressure from certain unnamed child-avatar activists who demanded to be kids on a continent plainly labeled ADULT ONLY.
Ultimately, kid avs who butted their way into Mature and Adult-Only areas through their "political activism" only muddied the waters for themselves and everyone else and now we all pay for it.
Rationally *applying* and *enforcing* LL's own rating system would have stopped, prevented, and clarified much of the "ageplay" nonsense right out of the gate.
But no - common sense policy has always taken a back-seat to hysterically-inflicted policy as a result of some RL legal case against LL.
Before the child players and their "parents" get in an uproar over tipping at their sacred cow - I stand behind it - kid avs should be restricted by LL Community Standards to G-rated areas, along with the people who want to play as parents of kids avs.
Want to be a kid or act line one, then why on earth does LL *or* your so-called parents take you to mature or adultonly areas... or worse... live in one, dragging their so-called kids with them.
Since LL can't or won't enforce their own maturity standards, it's fallen to the rest of us abuse report the kid for truancy or tresspass, and their so-called parents for negligence If you see a child avatar in mature or adult.
But who does that?
And let's call it what it is: anyone in a kid av is NOT roleplaying WELL if they demand to be a kid in a mature or adult-only area and then get upset with being kicked out.
Drag a kid to a topless bar or adult store in RL and tell me how it goes?
If you want to go to the nudie bar or topless dance club - become an adult first. DONE.
Since its all roleplaying, we should do what would you do in RL if you saw a young child wandering into a sex shop.
Holding the kids to actually acting like kids (rather than grown-ups in creepy avs) will end a lot of the nonsense right there by pushing the kid community to police themselves better.
Dragging their roleplaying parents into kids-court too will only provide more encouragement to RP correctly.
Many others have pointed out many "look-based" criteria, but every one of those has a fatal flaw: if you set a specific quantified value - someone will find a way to "game the system" in a way that causes problems when specific policies are literally applied.
Now, here's the super-tricky part - what about adult avies who want to be child-like?
For example - the Lolita fashion wiki link posted earlier showed adults dressing child-like for whatever reason.
Legally - they are still adults even in childlike clothes.
How many Halloween costumes in RL would qualify as "ageplay" in SL terms?
Or New Years costumes for that matter.
Someone else mentioned diapers - which should not even be part of the ageplay discussion without suddenly lumping everyone who is incontinent into an "ageplayer" category, which most would find insulting, as well as some in the BDSM community which has been known to use them for certain scenes having nothing at all to do with under-18 behavior.
So, here are some thoughts to make it unambiguous:
As far as criteria go, the *first* criteria for any "ageplay" investigation should be: sim rating.
Basing the "subjective" child-or-adult rating should include the location where the avatar is.
G-rated? bias to assuming, subjectively, that a child-looking av IS a child, since that's the only rating where children avs should be playing anyway.
Yes, this also means expecting kid avs and their families to keep their activities on G-rated sims. End. of. story.
The *second* criteria should be "are you roleplaying as someone under 18?", as an explicit setting right next to the "maturity rating" a user/Resident chooses to see.
LL could also add third unambiguous criteria of "age-rating" to shapes and clothing as a settable attribute.
You know how items say: ages 18+ or ages 3-6 - let designers set that explicitly on things they design.
For shapes you could add the age rating to the shape settings like gender.
You create a shape, and you set the avatar gender AND apparently age, while wearing that shape.
Otherwise, the apparent age defaults to "NONE" which has various effects depending on sim rating as described above.
Then, LL would have data to make much more consistent determinations of age violations than the "ad-hoc, at-whim, subjective" rating "system" they haphazardly apply now.
The real message should be that no one should have to guess.
Allow for specific settings and you have specific information to act on.
Plus, you could have some additional benefits/features such as auto-muting any under-18 avatar.