Starting a funded PhD at 38 with a mortgage, what did the age gap actually change day to day

On the younger advisor: set it up explicitly in the first month rather than letting it be awkward for six years. Say out loud, once, that you have industry experience and no academic experience, that you expect to be supervised as a student and not as a peer, and ask how they want to be told when you disagree. Junior advisors are often more anxious about supervising an older student than the student is about being supervised, and naming it defuses the whole thing. The pairs I have seen go wrong went wrong because the older student quietly behaved like a colleague and the advisor quietly resented it, and neither said anything for two years.

Mild disagreement with the framing that the social side is a problem to solve. Treat it as a job, turn up, do good work, go home, and the cohort question quietly evaporates. I did mine in my thirties surrounded by people ten years younger and the friendships I made were with two postdocs and a technician, all of them roughly my age and stage, none of them in my cohort. The cohort is an artefact of admissions, not a friendship group you owe anything to.

Started at thirty six, finished at forty two, and the honest summary is that the age gap was the least significant thing about it. What was different in a good way: I had run projects before, so I could scope work, say no, and read a room in a meeting, and those three things are worth more in a PhD than raw cleverness. What was different in a bad way: the cohort bonds over being broke and free on Thursdays, and I had a mortgage and a school run, so I was never going to be at those pub nights and I had to build my social life around the department rather than inside it. The thing nobody warns you about is that you go from being the person who knows how everything works to being the person who does not know how anything works, and that is a genuine ego event around month four.

The cost that actually mattered for me was not the stipend, it was the years of pension contributions and salary growth that did not happen, and I only sat down and calculated it in year three. That does not mean do not do it, it means do the calculation now with a spreadsheet rather than discovering it later with a knot in your stomach. Also budget for the fact that the finish date on the offer letter is optimistic in most fields, so run the numbers on the honest length rather than the advertised one. If the sums still work, they work, and you will never again wonder.

Older students in my department finish at a higher rate than the twenty two year olds, in my entirely unscientific observation, because they already know how to work when they do not feel like it. That is the whole skill.