question about age relation dni's

I've been seeing a lot of 'people under the age of 15 dni' or 'people over 18 dni' type of writing in bios
and I'm sorta wondering why?
especially because these profiles aren't very risque or inappropriate and I really doubt these people are starting s3xual/romantic relations with underaged myspace users or somethin
Dunno, it just seems weird
would you not interact with people outside of your age range in real life? what's the issue?
someone explain it to me it seems kind of weird and performative