I knew someone in her 40s who'd been a veterinarian, went to med school, did 2 years of an orthopedic surgery residency
then switched to an internal medicine residency. She didn't seem all that happy with her decisions.
Truthfully, medical school won't be the problem. Residency will be where the individual will regret it.
Unless that person can't possibly see him or herself as anything but a doctor it is probably a bad idea. Due to a variety of reasons a LOT of new docs regret going into medicine. It would be a really bad idea if someone already had an established career doing something else.