Should 16 year old males have to pay rent to their parent?

I’ve been with my fiancé since we were 15. When he turned 16 his mom said he needs to get a job and start paying rent since he is old enough now to support himself.

He has 2 sisters who do not have to follow these rules and pay rent because they are girls and his mom says a man needs to take care of things.

He payed her rent all the way from 16 to 21 when he moved out and we got a place together. His sister is now 24 and still lives at home with the mom and is not required to pay rent because she is a woman and not a man. (She also has a great job and makes really good money).

My fiancé is really resentful about this and we don’t think it’s fair. What’s your opinion is this fair or not?