@LeGaosaure my gut reaction says: put an adult rating on any kink, regardless of whether it's sexual.
Kink is an adult thing, in the sense that it requires understanding and consent for things that kids can't usually understand well or consent to. And also: adults should not do kink activities with kids.
What's your thinking around not wanting to play into the idea that kinks should automatically get an adult rating?
(I'm genuinely curious and not set in my thinking about this. Haven't really thought about it much before.)