Consensual relationships don't have to be "healthy"

 Stigmatizing or pathologizing people's sexuality or relationships between consenting adults is neither feminist nor liberatory.

Yes, 18 year olds count as adults. There's no such thing as an age when "the brain is fully mature." Treating young adults as extended children who need to be protected from their own choices is linked to ableism, sexism, and racism.

Yes, calling sexualities or relationships "unhealthy" counts as pathologizing.

"I don't want to know about your sexuality" or "I don't think it's a good idea for Jordan to date Taylor" are valid.

"Your sexuality is unhealthy" or "It would be unhealthy for Jordan to date Taylor" are pathologizing. Don't do that.