This “age doesn’t matter” stuff is nonsense. No, 34 is by no means too old, but you’re going to be 40 when you’re done (roughly), having lost 5–6 years of prime earning. Oh, and the personal cost; there’s always a personal cost. You are now 40 and Dr. Question Asker! Congrats. If you’re in the sciences and want a treasured position at a research university, you’ll spend the next 4–10 years as a postdoc. In some fields, like computer science, the opportunities are high, but that’s not most fields. It’s not completely unreasonable to start as an associate professor in, say, biology, at the age of 50, but then you have six years to prove yourself (tougher at some places than others) and warrant tenure. But you’re awesome and tenure is granted. Great! Now you’re 57 (the tenure evaluation process alone takes a year), so you have maybe a decade before you start to think about retiring. And that’s not the worst-case scenario. The odds are not far from 1:2 that you’ll finish. Most people leave of their own accord, but often after completing 2+ years of coursework and 1+ years of research and deciding they don’t like research and can’t do it anymore. And while things could go better, there’s no guarantee of tenure at a research university (single digit percentages of PhDs get tenure-track jobs at research universities and get tenure).

You could potentially go to a teaching school. I think I will be forever grateful that I did. If all works out, I might have tenure and still be in my 40s. I don’t make a ton, but I’m also nowhere near poverty.

If you’re in the humanities… well, you’ll go back to whatever you were doing before the PhD, or possibly try to eke out a living as an adjunct.

Am I discouraging you from going? No! Well, sorta… I did not get good advice. Most people don’t. I don’t per se regret my decision and I love my career, but I wish I had known more. I wish the system treated people better. And I’m thankful I’m in computing, where jobs are plentiful. I know some people who make good livings helping fellow PhDs find jobs/careers outside of academia, and trust me, these people are earning their keep.

Make sure you have long talks with people who’ve been through the process, didn’t start within 5 years of undergrad, and are in your discipline. This needs to include people who didn’t finish, or else you’ll have selection bias (you’ll only get one side). There are plentiful discussion boards to find people and info. Make the decision, but make the decision from an informed perspective. If this is right for you, it can be wonderful (and horrible, sometimes).

If you are 50 and starting a PhD full-time with the intent of changing careers? I can’t say that I think that’s a good idea. So go forth and decide within the next decade.

Source: https://www.quora.com/Is-it-too-late...rt-a-PhD-at-34