Shifting your forum's main audience

Consider this: Your forum isn't targeted towards a young age group in any way, but it has turned out that your community has become overrun with teenagers and children who act immaturely, and have diminished the quality of content on your forum.

How would you go about shifting the main audience from these younger children to adults and a more mature crowd? Would you place stricter limits on age validation upon registration? Would you remove "fun" features in order to make the site less appealing to younger members, but more appealing to those who came purely for information and conversation (older, mature members)? How would you tackle this dilemma?

 

Personally, I'm not sure, and that's something I'd personally like to try with my own forum.

 

I had that once. A more strict view towards spam, posting games (eg. snake with words) and a pointsystem that rewards serious posts fixed this pretty much