Hi @Ruth1362
Hmmm...you are wise to use caution here; especially if your property is near the beach and is known for spring break partiers. Is this a new guest to Airbnb? Do they have other reviews?
Guests cannot create a profile if they are under 18yrs old. Airbnb is supposed to verify their ID. It's good you added your age restrictions to the listing, but can't go back now and cancel the reservation on that basis. You can express your concerns that the guest is not 18yrs old to Airbnb. Guests are not allowed to misrepresent their age per Airbnb Rules, but people do use fake IDs at times. You are allowed to ask for photo ID when they arrive, but only if you have disclosed that on your listing in House Rules:
"The Host may ask for ID after booking if the requirement is in the Host’s house rules at the time of booking, or where required to comply with applicable laws or contractual obligations applying to the Host."
If you are not able to get Airbnb to cancel the reservation, I would send a message to the guest "Welcoming" them and advising that you don't allow parties at the property and only registered guests are permitted. You can then require that they add all their guests to the reservation. You can get Airbnb to cancel the reservation (without penalty to you) if you have proof the guest intends to break one of your House Rules.
Security Camera Disclosures
I would also update your security camera disclosure under the Guest Safety Section as you don't have the required wording that meets Airbnb policies. You need to add whether an active audio/video recording is taking place, the number of cameras and where they are located. It can really be an issue if the Guest does try to hold a party and you contact Airbnb. One of the first things they look at is your proof there was a party (camera video). If your cameras have not been properly disclosed, your listing can be suspended. Reporting parties to Airbnb can also be a "Catch 22" for Hosts. Usually your listing is suspended while they investigate.
Informing Guests About Security Devices
https://www.airbnb.com/help/article/2914