Same as almost every other career in the medical profession—4 years of undergrad, 4 years of medical school, and then at least 3 years of residency. And that doesn't mean proving that you’ve lived in the state of California for the past 3 years. You will be almost 30 before you make your first dollar and likely have a bunch of debt.
Also, as you're dealing with a lot of families, it's especially important to have a heart of gold. Just knowing your stuff is not enough—you have to make people feel better about their physical condition, even when you know there isn’t much to feel better about. In that sense, you're almost like a paid actor, which might be a difficult concept to wrap your head around.