As someone who used to run a forum myself (
rockmetalforums, now defunct) I believe I can say with some authority that simply humiliating or insulting a user does nothing but create future problems. If your intention is to irritate someone until they leave, you might as well just delete the account altogether, it's much faster and forumwide saves everyone about 40 psi of bloodpressure. Especially the mod squad.
Also on the point of imposing an age limit - yes there would still be the occasional idiot. But Max, as you pointed out yourself, there would be a lot less of them. This is the whole point. Reducing the numbers of idiots. The fact that we can't 100% eliminate the problem of idiots signing up to the OWF, doesn't at all mean that the plan is a failure and not worth implementing - saying that would be selectively perfectionist against anything that you don't want. No individual initiative to reduce the numbers of morons registering for accounts will be 100% - they'll all need backup initiatives to catch the ones that slipped the net.
The age limit is just one weapon in a war against idiotic spammers. You've got the entrance exam, multiple warnings, and the age limit, all working together. I can see this drastically reducing the amount of clipwing dipshits we get each year.