- Full time commitment seems critical to the process. A Ph.D is a time of intellectual exploration, and you can't really do that fighting work and family deadlines.
- On the other hand, time can be squished for older people by virtue of industry experience making them more efficient
- I'd be hesitant about remote, since so much of a Ph.D is learning from others. Hallway conversations are critical. That's possible remotely, but not common.
- Fully agreed about "side activities." Teaching is fine -- you learn A LOT from it -- but a lot of Ph.D programs give stupid administrative grunt work. The metaphorical cleaning of test tubes on a professor's project is a serious red flag.
No such thing as too old, but having a mortgage and family myself now, I definitely get much out of a Ph.D program right now.
I'll mention too: If I didn't have a Ph.D, I'm mature and disciplined enough now that I could learn the same without a formal program.
I am skeptical of new world "accelerated" programs, which often have little substance, and are designed to milk working professionals. It's like getting the piece of paper in Wizard of Oz.