30 years old here and starting the prereqs for RN next week part-time (online). I figured at this age I don't have the time or mental acuity to be a MD. My first class being A&P should be a tell-tale sign of whether this experiment will go well.
The tricky part (for me at least) is the memorization. After 20 years of working in a field where I can look up everything I need to know, suddenly I had to commit thousands of data points to memory to pass a test (then promptly forget the data afterwards). It's an archaic system.
Anyway you'll have to find a way to memorize and regurgitate. If you can do that, the rest is just common sense.