I'm probably going to go back to get a PhD at some point in my 40s. Not because I want to become a professor, but because I think it'll be good to sit down for a period of four or five years and just think in the company of other agile minds.

Of course, this is only possible because I'll have made sure to have had an entire career behind me, and I will not be worrying about putting food on my family's table or keeping a roof over their heads. A PhD is to me, therefore, not a profession but an avocation. Something to do after you've done everything else. The idea of doing it a few years after college, with the intention of making academia your profession? That's terrifying to me.