Hi @Julie984
When you signed up to Airbnb as part of the terms you signed you agreed not to discriminate against guests on the grounds of race, religion, sexuality, sex or age.
Obviously if there is a legal reason i.e. your housing association or complex doesn't allow it, that means that you can't host this age group ie 18-25's then Airbnb will back you up. They won't if you are simply choosing not to accept having youngsters as guests..
I think it is rather rude of you to suggest that hosts who accept youngsters are only in it for the money or don't care about their homes. I have had over a hundred young people stay with me who have been under 25. They have all been delightful including a young couple who took me out to breakfast, another who bought be a candle when I stayed up late to check them in when their flight was delayed and another who helped carry some heavy items up the stairs for me.
I am happy that Airbnb actively advocates that hosts shouldn't discriminate and see no reason to lobby against this. After all, why would I sign up to host with them if I didn't want to abide by their terms?
There are other platforms that I believe you can put age restrictions on, perhaps listing there would better suit your needs @Julie984