I met one nurse who was in medical school (actually, at the my former teaching hospital). She used to be an ICU/CCU nurse. As a medical student, she was excellent with the patients! Treated them like people and not "Mrs. Kidney Problem" or "Mr. Neutropenia".
I don't think it's ever too late for learning. There was one medical student in his fifty's who not only was smart, but was also wonderful with the patients.
I have a probably snob-ish opinion, but here it goes:
I think that "kids" that graduate from high school, then go to pre-med school then go to medical school make the worst medial students (from a "providing compassionate healthcare" point of view). In my books age does make a difference. Not that these "kids" weren't smart. I've met very smart medical student-kids. I learned a lot of neat medical stuff from them. And I appreciated the education! But when it came to providing that important extra compassionate touch to their medical care, the medical student-kids were very lacking. . . . simply because they never experienced a great depth of life. Heck, they barely learned how to manage to live independently much less learn how to provide emotional support to patients.
However, one is never too young to learn! Some of these medical student-kids did end up becoming compassionate physicians.
Nurses can and do make great physicians if they want to go that root. Likewise, adult medical students (thirtysomethings and over) can also make great physicians. It's never to late to learn. I guess, it's also never too "early" too learn as well.
Another thought. An alternative from nurse to physician. . . . become a NP?!?!?!?