I started my PhD in science-based archaeology, analysing mediaeval artists' paint, at 35, after a somewhat interrupted educational career. After A levels I dithered over degree, plumping for Physics. But I dropped out in the first year, largely due to drink, loose women and lack of commitment. Unqualified, I drifted into sound engineering, then communications and IT, learning on the job.
At 29, fed up with being on a career ladder that only had one rung, I started a degree in Art Conservation at Camberwell College of Arts. Conservation suited my interdisciplinary temperament, combining hands-on practical craft restoration skills, history of art and of technology, a lot of chemistry, environmental and materials science, and a little biology. I became fascinated by works of art as physical objects: the identification of the animal, vegetable, and mineral components of paints, or of plant fibres in paper, wood identification and dating, and the many spectroscopic methods that have been adapted for nondestructive testing of historical and archaeological artifacts. Consequently I went on to do a part-time MSc in Conservation Science, at De Montfort University, which concentrated on exactly this kind of science.
My decision to continue on to the PhD was largely vocational dysfunction (i.e., I couldn't decide what to do for a job) and partly liking the idea of continuing the research I had started on my MSc. The lack of suitable jobs at that time was also a major motivator: Most were aimed at the desperate-for-experience early-20s, pitifully paid and fairly menial. I'd get as much money on a PhD grant, so why not?
There are advantages to being a 'mature' student. You are often referred to as 'Doctor', as it is assumed that by your age you must be, which is actually quite motivating, as you realise it feels good. You tend to be mistaken for staff, or at least treated as a peer by academic staff. This is fantastically beneficial. It is much easier to ask for things, advice or favours, and to get them. You tend to be treated more seriously. For example, I have had a book and all the papers I have submitted accepted for publication practically without question, which I seriously doubt would have happened if I was 21.
The world-weary cynicism of old age can work in your favour: In particular you know how to lower your expectations. Rarely do students actually fulfil the vast, ground-breaking, world-changing plans stated in their PhD proposals. (Wise Words: If at first you don't succeed with your research, redefine success.) Keeping motivated is hard for all PhD students, but years of work experience do at least teach you that a large part of any job, however wonderful, is drudgery: Employment happiness seems to be about perfecting the nondrudgery part. This realisation makes working through motivational slumps easier. If you treat the bad parts as a job, and just plug away for a while at 9 to 5, Monday to Friday, you will at least keep some momentum. (Wise Words from my supervisor; thanks!) On the other hand, you do think, well if it's horrible, I may as well quit and get a proper job.
Less seriously, after a working life you really appreciate lying-in in the morning, and no longer having to wear a tie. Oh, and the stimulating company.
Of course there are disadvantages, too. Initially, learning new stuff is harder when you are older. The first few months of going back to study are absolutely exhausting: I loved it, but felt hopelessly inadequate to the task. Fortunately your brain does kick back in and brushing up the maths and chemistry you learnt in school is a thousand times easier than learning from scratch.
Age can be a very real obstacle to career development. There is a certain ageism in academia and many junior research positions have age limits. This has become less common over the last 3 years, at least on the forms, but I suspect that the age criteria are still applied just the same. Another handicap is unreasonable expectations: Even if you do get offered a job, it will be a job intended for someone of say 25, with the accompanying responsibility, challenge, and salary appropriate for a 25-year-old. At the risk of seeming greedy, it's not enough, when you are 38.
The biggest problem is the drop in income. For me, adopting a student lifestyle was never an option--I just didn't fancy acting 21, living in hall, bopping till I drop, and generally being the oldest swinger in town. Not every night, anyway. Downshifting financially can also be hard on your friends and loved ones. You and they have to get used to you not really ever having weekends and evenings free from the nagging PhD work. Your partner can't chuck her job and have babies. (This is a problem when you are in your 30s.) And it is hard to go out to play with your old friends, as they simply have more money.
You can make big savings with small changes. Let out the spare room, learn to cook, cycle. You quickly realise that this is not worse than you are used to, just delightfully different. My other strategy was to keep my lifestyle the same in quality, but not quantity: when you go out to a restaurant, or go on holiday, do it to the same standard as before, just do it less often.
At first I supplemented my grant with freelance sound and IT work, as I had during my BA and MSc, but the further you get into your PhD, the less time you can spare. I am, therefore, now more financially strained than for a very long time, which puts me under great pressure to complete and write up before my funding finishes. That said, you can't study 24-7, and the odd few hours or days of different, paid work makes you no less productive overall. It allows your brain to cool down, and often you clarify your ideas as a result.
Perhaps more could be done to ease the lot of the mature student. I personally think mature students do make better students, and they should be encouraged. Although I appreciate that you might not want to invest heavily in someone who has only a few productive years left, it is difficult to say when the cut-off point might be. My funder, NERC, does pay a mature student's incentive, but it is only about £1500 a year. They're never going to pay me £20,000 per year to do a PhD, but at least making fees tax deductible would be a huge step in the right direction. An extra PhD year--even at the current grant rates--would at least make time for enough part-time paid work. (Presumably childcare would be good too, but it's not at present a problem of mine).
What next? After my PhD I'd really like to continue my research, indefinitely. I moan like hell about it, but I'd rather be doing this than anything else in the world. How will I do this? I don't know, and I worry constantly.
So to a prospective 'mature' student, what can I advise? Is it too late? No, but it gets progressively harder. The best advice I can give is, probably, get your qualifications while you are as young as possible. To any prospective PhD student, all I can say is: It is an incredible roller-coaster, loving it and despairing of it, and I have no idea if it is worth it in the end. My real advice has to be: Don't do a PhD just to get the kudos. You have to want to do the actual research--the process is what it is about.