Like to be able to use it when not rented, two young adult kids and their beaus.

Simply because they are innocent and cannot help themselves like a full grown adult

Well a rooming house properly run will never have vacancy but its running one such that you don't get shut down by code enforcement, then you owe the morgage and no income.The zoning that is common is;  3 unrelated adults. 

I am 60 years old with a husband and 3 adult kids.

I didn’t do parents as a co-signer (I don’t want to communicate with extra people) but I required them, or some other responsible adult, to be a parent guarantor.

I hope you lived here pre-COVID so you got to see how many community events Grayhawk hosts for kids (and for adults, but mostly for kids).

He will get a crash course in how real estate and real estate financing works, how to be a tough but fair landlord, and also how to adult.

Is he asking for a puppy or an adult dog?

Usually its adult dependent family member needing way too much help all the time. 

Anyway, I know a good half dozen young adults under 20 in Michigan who invest.