I think its up to the individual families to decide. In this day in age, not everyone can swing a $2,000 house payment, especially flipping burgers at Mickey Dees.
No, not everyone makes $15 an hour so living with relatives until you find someone to live with or a good cardboard box under the bridge sometimes is the only option.
And furthermore.....
In lots of countries, most relatives NEVER LEAVE HOME!
Why do they need to have a $2000 house payment?
That's my biggest concern, what happened to just renting a place?
Everyone is like "oh but I can't rent a place as nice as my parents"...
no shit usually.
The thing that always gets me is they all talk about how they are doing it to save money...yet they never have any fucking savings. I know dudes going on 15 years at home and they have the nicest cars, go out every night, but don't even have 401k's.
They end up dating 18-19 year olds in the 30's and have to fuck them in their cars.
It's retarded.
To answer the question, there is no maximum age; however, it should be short-term and with a goal.
Lose your job, by all means move back home and regroup.
Get thrown out/divorced, move back home until the dust settles.
If you are doing this more than a year or two, you haven't grown up yet.