I am not a law type, but I would believe that any adult could check in and...I believe that would be 18 years old. For a hotel, or a jurisdictions - city, county, etc. - to impose different would seem to me to be age discrimination. Now, besides the age issue, credit might be a problem. My 25 year old son does not have a credit card and without a credit card it is very difficult to check into a hotel! But, for age, I think nationwide you are an adult at 18. Any comments?
Yesterday my son try to check into the Courtyard by Marriott in Key West, he was told that he had to be 21 and was not allowed to check in, I had put a deposit, I talked to front desk person they told me no deposit was paid for room I then went and check my cc statement and deposit was charger, I now have to deal with CC and Marriott to get this reversed