Babygate
To restrict someone under the age of 18+ from doing anything or to leave them out of activities simply because they are not 18.
This includes swearing around them, making any innuendos, etc.
John: Hey! Let's go to the park or something.
Stephanie: Uhh.. No thanks.. I'm not going anywhere with Lucas, he's 15. We'll get in trouble.
Lucas: You're just going to babygate me because I'm not 18?