I started my PhD in my mid-30s. I was working as engineer support staff at a science institute at the time and was encouraged to enroll in a PhD course. I dropped out of the course and academia all together after 5 years for various reasons, among others being burned out and developing health problems. I would describe myself similar to you, loving to do research and working on hard problems, but that's just a part of getting a PhD.

I strongly suggest reading the "How to Survive your Doctorate" [1]. It goes into social, financial and office politics side of doing a PhD. You might think that it's something you can avoid, but it's not. It's a book I wish I've read before going down the PhD route.

[1] https://www.amazon.de/-/en/Jane-Matthiesen/dp/0335234445

I've done that, mostly because my position felt stagnant and repetitive. Some things to keep in mind:

- It's a full-time job. Unless you're really brilliant, or your current position has a huge overlap with the research you want to work on, expect to drop your current position.

- You have a steady income at this point, so you're not in a rush. Be patient and research where to apply.

- If you can use your position to first network with your future advisor, do it. Can you set-up some small collaboration relevant to your current position? Even better. Trust can get you a long way, and lift any doubts.

- Your strong card is that you will probably need much less "babysitting" than a younger student. Play that well.

- Writing is essential part of the PhD. If you already have strong technical writing skills, that's a huge advantage.

- Find a PhD that involves the least amount of exams possible. It's fine to attend courses if you find the topic relevant to your research, but being forced through an exam routine may not sit very well if you're already in your mid-30s.

- Post-PhD industry job opportunities typically arise through (paid!) industry internships. Make sure to complete 1-2 of them, even if that will add to your PhD time.

I currently am both a full-time employee and a full-time PhD student at a US university. Recently I finished my coursework and passed a qualifying exam so now I"m a "PhD Candidate" which means I can focus more on research.

It's been very difficult to do both school and work simultaneously. It helps that I enjoy learning the material and have had some truly outstanding professors. The biggest challenges for me have been (in no particular order):

- Group assignments with unmotivated or unethical students. In 3 separate instances, I caught a student in my group attempting to submit blatantly plagiarized work (simple GitHub search to find the duplicate code). Other times I would be the only person to write any code that actually worked.

- Seemingly pointless bureaucracy, like a form certifying that I completed all my coursework which needs approval by 5 people and a minimum of 4 weeks processing time. As far as I can tell, this form only asserts that I passed >90 hours of coursework, which is already in my transcript.

- Not enough one-on-one time with my advisor.

- Not enough guidance on the publishing process. I have collected anecdotes from some professors and snippets from my advisor, but I would have appreciated some formal training. I would have gladly swapped some independent study credit hours for a course about academic publishing.

On the plus side:

- COVID restrictions forcing classes to be online really helped with logistics.

- I used to have imposter syndrome pretty bad. But comparing my work to that of other PhD students across a broad range of topics has proven to me that I'm at least better than average for this university. Maybe I am a big fish in a small pond, but some of those peers have FAANG jobs now. So maybe I'm actually getting pretty good at this stuff.

I worked for four years and then went back to do a PhD, so I did it married, with a mortgage, and a baby, etc. was stressful in some ways but in others I was more mature so more self-aware and relaxed. I didn't have a problem getting a job afterward.

Your real world experience is an advantage, try to position yourself among relatively young scholars (recently tenured) and write one paper and submit it before entering grad school.