Boards that have 13 as the minimum age are more likely to be all or mostly 30+ if they have been around long enough, after a certain point. They almost never get new (younger) members.
Proof:
NeoGAF
Resetera
GameFAQs
IGN

Boards that advertise as "adult" are more likely to continually solicit new younger members, who want to make their identity an adult one.

Stop getting angry and offended online in your country

>>40550837