https://arstechnica.com/science/2017/05/the-older-the-doctor-the-higher-the-patient-mortality-rate-study-finds/
I think this is also due to the fact that older doctors don't have to go back to school to learn new techniques.
I've thought about that a lot. Once a doc enters practice, there isn't much time in the workday to stay abreast of the latest. I've read that they tend to rely on pharm salesmen, journals, and the occasional conference/seminar --don't know how true that is, though.