Hi there,
I started out as a pre-graduate student Analytical Chemistry major. At the time, I had no interest in medical school. My undergraduate degree was totally paid for by scholarships, my Ph.D was totally paid for by scholarships and department research stipend. When I entered medical school, I had no educational debt and had never borrowed money. I received a full-ride tuition scholarship for medical school and only borrowed for living expenses. I have deferred payment of my medical school loan until end of residency because the interest is so low and I owe less than $50,000. I was far older than 30 when I began my Ph.D work and still older when I began medical school. It can be done so age is not a factor.
If you are in an MD-Ph.D program, you need to meet the requirements for both programs. Your tuition will be paid by the department that accepts you. You will be providing research and publications for your institution so you become an asset for them. MD-Ph.D scholars are expected to maintain higher averages than MD students because of the scholarships so keep this in mind. On the other hand, you get a nice quiet office to study in, your own lab-work and in my case, my own lab (heaven on earth) and very generous library priviledges as I had the title assistant professor once I had passed my qualifying exams for my Ph.D. Since you will be spending far more time at the school than your MD candidates, you have a few extra little perks to keep you comfortable. All in all, not a bad way to go and doing research is great fun no matter what age. I also had a great relationship with the faculty both pre-clinical and clinical as I was often tutoring students.
The bad side is that you will be spending more time at school and away from your family. You just have more work to do and you start with one class and graduate with another. You become very intolerant of people who waste your time in any way. (Some people have referred to this as arrogance, I refer to this a practical.) Your colleagues will often be much, much younger too but again, this is not necessarily a bad thing. (I enjoyed working and learning with my younger colleagues).
njbmd