1900 because that was when "the servant problem" arose, the problem being that nobody wanted to be a servant any more. But in some contexts the dynamic is maintained.
I may be off by plus or minus three decades. Maybe 1930.
What are you talking about? Restaurants don't have any trouble hiring people to work there, as long as they pay enough. No one minds being a servant if they're getting paid enough. Of course, it's not a terribly glamorous profession, and you can get more pay doing something higher-skill, but that usually requires much more education and training, so working as a server appeals to people without that.
I'm sorry, I just don't understand the point you're trying to make here.
I may be off by plus or minus three decades. Maybe 1930.