A little bit about me: I’m 31 years old and have had medical school on my mind a lot these days. I would love to be a doctor (and would be happy in a number of specialties) but have all the usual worries about my age, finances and even chances of getting into medical school.I have a PhD in biochemistry and have worked for a few uneventful and unproductive years in research. I’m wondering how realistic I’m being regarding my goals and dreams and would appreciate any and all feedback.
Hello, and welcome to OPM! I have found this to be a place of great encouragement and inspiration; I hope you find it to be as well.
To address some of your concerns:
Age: First of all, at 31 you’re not old. 
You can do this if you want to, in terms of age. (I’m almost 29, not much younger than you, and just starting a post-baccalaureate pre-med program this fall. And if you search the OPM boards, you’ll find plenty of people in their late 30s, into their 40s, even some in their 50s doing this. So take heart!)
Finances: Yes, medical school is expensive. But if you are willing to live on a budget, the loans should be able to get you through. Especially because the amount of loan money available for med school is much greater than for other degrees. (I’m not in med school, but this is what I’ve heard.)
Chances of getting in: Ah, yes … getting in. I don’t know your background, of course. But with a PhD in biochem, you clearly have a lot of the science needed for it. You have also done research, which is great. Then there is the MCAT, of course. I’m not sure how fresh you are on orgo or physics, perhaps you might need to review some of that? I don’t know.
You would need some clinical experience, clearly, and some volunteer experience (you could also combine the two and volunteer in a clinical environment). Shadowing some doctors also would be a good idea. Basically, you want to show the admissions committees that you know what doctoring is about, and that you know you want to do it.
Really, it comes down to a decision. Do you want to do this? And if so, are you willing to make the leap? And the sacrificies necessary? These are not easy questions to answer, and I had to wrestle with them myself. But if you do decide in the affirmative, it is possible.
Spend some more time on the OPM boards (if you haven’t already), read the diaries (they’re very inspiring!). Get more information to help you make your decision. Best wishes to you!