A close friend of mine from grad school went back to get her PhD at 56. She moved across the country to do it, including living away from her husband (their children are grown), and subsisting on the same $20k a year assistantship as the rest of us. She will hopefully graduate this year at 61 and is applying for faculty jobs now. Her situation was a bit unusual, as she had met her advisor at a professional development training, and her advisor strongly advocated for her to get in (she had wonderful experience working in the field and some adjunct teaching experience but no real research experience). The research learning curve was a very steep one for a while, as was being back in school for the first time in 30 or so years, and the massive pay cut she took. But it was something that she really wanted to do, and she had her advisor’s complete backing every step of the way.