Moose, the law isn't something you get to make up. The only thing you are right about in your post is that hotel tenants are not the same as the situation we are describing. You are right, hotel tenants have MORE rights than the son we are talking about. I appreciate your analysis but you have absolutely no law to back you up. You can't make it up out of thin air..... What worries me is you are a police officer and should know better.
Temporary is an ongoing understanding that is controlled by the homeowner who has all the rights. If they let you stay for 6 years it could still be temporary. The legal definitions say that term is based upon the period "when rent is due." Not when Moose thinks you have been there long enough to now qualify. As you said this bothers me, chiefly because you should know better since you enforce the law.
Now as I said, California might as well be a different planet so maybe you can be excused on that part, but tenancy is a legal concept not one of opinion. Feel free to find me anything that supports your opinion and I'll be happy to read it. I think you will find that your analysis is sort of an urban legend among armchair lawyers. If you stop and think about it for even a moment you would realize how crazy your theory would make tenancy laws.
Every time you let someone in your house there would be some imaginary date looming at some undetermined time in the future where you would suddenly lose control of your own dwelling! That's insane!
By the way, "I would still argue that the son was a tenant entitled to occupy the residence for free according to the oral agreement with his mother." That was not the oral agreement. She said he could stay until he got on his feet but that it was always to be temporary. Further, an oral agreement is not a contract without. . . . .. .CONSIDERATION. We call that rent. Until he pays rent, or utilities, or something in exchange for his place to stay then he is simply a transient guest. You can not find a single word in the LAW that supports otherwise, at least not Florida law. I have no idea bout CA.
It's important because I wonder how many other phantom laws you and your compatriots are out their enforcing! This isn't a deep legal concept. Property rights are. I have provided you with the law. In Floridia there are three levels of residency: transient occupancy which can be paid or unpaid (guest or hotel), tenancy (which is ONLY triggered by payment of consideration in the form of rent/utilities), and Ownership (which is signified by a deed). Conspicuously absent is the "Moose said they have stayed here long enough to be a resident statue!"
Again, I'm smiling as I write this. I'm not trying to be angry or rude, but really Moose, this isn't even a question. Her son is NOT a resident after he turned 18 and isn't paying rent. Law is just law, if you can't find it written somewhere it doesn't exist.