Just out of curiosity, doesn't 13+ include 65- as well? I remember reading something about "posts I wouldn't want my grandma to see etc." (Don't know about you - but my grandmom would flip if she read half the posts on the Debates Forum ... )
"This is not because of the forum content alone, but also because the very nature of correspondence chess requires frequent private communication with strangers.
"This also allows us to comply with COPPA (Children's Online Privacy Protection Act) because we do not want to seek parental consent for every minor that attempts to join this site."
To comply with child protection legislation, Russ either has to seek the consent of the parent(s) of each young person who joins the site (and I think we all understand that he cannot afford to do this), or he has to take steps to exclude people who are under 13.
Excluding young people may make forum management easier, and that may have helped make Russ's mind up, but in the long run, he may not have had much choice.