@Karil7 What @Lisa723 told you is precisely correct, if you carefully read the actual terms of the discrimination policy she linked:
- Airbnb hosts may not:
- Impose any different terms or conditions or decline a reservation based on the guest’s age or familial status, where prohibited by law
Everything you need to know is in those last 4 words. You may have a case if you live in a jurisdiction's laws meet both of the following criteria:
1. Individual Airbnb properties (rather than access to the platform itself) have the legal status as public accommodations
2. Private establishments are prohibited from setting a minimum age for entry
I don't know where you live, but this combination is very unlikely. Like unicorn-level unlikely.
But even if you did have a case for a complaint, Airbnb's legal team does not have the authority to force a host to rent their private home to any person they don't wish to. So there is no course of action available to you here that would actually benefit your (legally adult) child, except to help them find a more suitable accommodation such as a hotel, hostel, or campsite.