Former physician (nephrologist) here. I quit medicine in 2008. I find your question a little confusing. Like others I question why you want to learn how to code. I mean, I guess it comes down to what your plan is. I realize we are on hacker news but startup doesn't always equate software company.
Uptodate was started by a Burton Rose, a nephrologist. I don't know the history of that business, but I doubt he sat down and coded the website himself.
Presumably, the value of you working on a startup is related to your medical background, and the expertise that entails. Not spending long hours of not-much-free-time trying to learn how to become a mediocre programmer. I don't see how your changing the world is going to be based on your programming skills.
The converse situation would also make little sense. "I'm a skilled programmer of age 35 who wants to create a medical record start up. I'd like to learn how to diagnose patients in my free time..."