Do you know what the age minimum to rent a room for this location is? Can I stay there alone at 18?

Yes you can. Can or credit card with a valid state DL or id

But you can go purchase a shotgun or rifle @18 just not a handgun just saying

I think 21 is the legal age

In Texas I think you have to be 18 and yes at 18 you are legally an adult except for drinking and purchasing a handgun