A lot of people end up in "dead-end" jobs, jobs that they don't really enjoy or are not paying enough to support their goals and/or family. People can work in jobs like these for decades before mustering the courage to change career. There are times where in that could happen after you reach the age of 50.
We do believe that there is a guide on this site referring to how to successfully begin a career change, that's a more general view on this matter. If you want to check it out, I would recommend it. Anyway, here's How to get started on a career change after 50.