Quite understandably your dad feels the urge to do other than he’s doing, but there are a vast number of things he can do at age 49 that make more sense than attempting a physician’s career.
It sounds like a lot of the driving force is his desire to escape his current job. Obviously he can quit his job - you have the money that can remove him from it. Perhaps you can let him take some time off from the torture job, so that in a rested and less harassed state he can explore the array of alternative things he can do that make reasonable sense.
I think that when you’re an older person there is especial suitability of educational tracks that you can quit at any point and still get notable gain. Computer science has this quality - just from learning a programming language you’re significantly advanced, but the physician track doesn’t - he wouldn’t get significantly occupationally advanced from doing the prerequisite courses for medical school.
Also, computer science doesn’t have the barriers that the physician or, indeed, all other academic tracks have. In the considerable research I’ve done for these forums, it is the only academic area in which I’ve found significant numbers of employers willing to hire on the basis of demonstrated ability alone. Technically you can teach yourself enough to be employable. Every other field has some point in the preparation process where the demand for candidates is exceeded by the supply. And, while your dad may have forgotten his computer science, prospective employers don’t have to know that. They will to a large extent value his CS degree, and your dad can encourage them in that. Of course, he will have to come up to speed in it. But even if your dad has to learn computer science from scratch, it won’t be harder than learning medicine from scratch, and he is vastly more likely with computer science to get successfully through the preparation process to employment.