I don't think it's just a question of age, but how long can one expect to get a rate that they find appropriate for the risks associated with this business. I highly doubt at 50 I could still make $4-500 per date MINIMUM, on a
regular basis. So for me, that would be my cue to get out...when I have to start lowering my rates while still being expected to deliver the same service.
I am like you Memory, though almost 30. I came to be a provider long after I had my first degree, 2 marriages, and a child, and after my Masters is completed, I will be ready for a regular 9-5 life again.