US and EU laws, donīt remember where. 13+ see EA UK forums and see lot of minors banned. (they need BOTH parents signed auth)
Some other countries allow 12 some other are more stricter, 16-18
That is the minimum, you must adjust your forum req to the content, mild swearing will increase the age req almost always
Well, that's an age requirement set up by a private company/corporation, so it doesn't actually count as a law (by law, I meant specifically something set up by a government to control who may post on and join forums). Rules like that are more likely set up not because there are specific laws for age requirements, but more because the company/companies/forum owners worry that they will be held accountable/responsible for members that get in trouble (e.g. a child who gives out their home address and phone number on a forum to a pedophile, taking flack from parents/consumers about "inappropriate" content, etc.) or contravene other (actual) laws while on the site. There may be rules in some countries (although I don't know any, but I'm not an expert on all countries attempts to control the internet) that have strict guidelines on what their citizens may legally do on forums, but it certainly wouldn't apply worldwide.
(Plus, as Pescado says, 12s are annoying as hell
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