In one of ReeseMcBlox’s posts she mentioned that not only is there already floodchecking for the same IP creating multiple accounts, there’s also already an age limit (and email verification) on posting comments and it doesn’t work – all that will happen is botters will create accounts in advance. As an added side effect, as @AbstractAlex mentioned, legitimate users will not be able to join groups. Sorry, but an age limit on groups won’t accomplish anything good.
With that in mind, you can have Lilly_S lock the thread if you’re not comfortable with others broadening the scope to stopping botting in general since age limits won’t work.
That ROBLOX has already tried captchas on part of the site and has specifically said they don’t want to implement them anywhere else should be a big clue that they don’t solve the problem. If that’s not enough, recognize how many bot accounts are being created still and notice that even though they have to solve a captcha they’re still getting through. Captchas are an idea that look really good on paper, and are nice for smaller sites, but any high-traffic site isn’t going to benefit from them.
5 seconds * the many times you post a comment, send a PM, or do anything social on the site. That adds up to a lot. Even if they’re not put into widespread use, captcha minigames are still annoying and certainly aren’t worth it since they won’t stop the botting in the first place.