When interacting with a system please always take the age of the body and the person you’re talking to into consideration and treat them like the youngest age out of the two.
If you’re talking to a 12 year old in a 40 year old body, talk to them as if they’re the 12 year old they are. If you’re talking to a 40 year old in a 12 year old body you still shouldn’t say anything to them that you wouldn’t say to a 12 year old.
If anyone involved is a minor you need to talk like there is a minor present, and you should absolutely never be in a relationship with an adult fictive in the system of a minor. If you’re also an adult it’s inappropriate for the minor, and if you’re a minor then it’s inappropriate for that adult fictive to be involved with you.