Total experience in the stock market: 20+ years.
Investing experience: just about 13 years.
Wandered through the entire Gaussian curve in that 20 year time period, too. 
I think the “rational theory” can be learned within a few years, but finding the psychological space where I feel totally mostly comfortable with my investment style took me another few years (and I thankfully had the tailwind of COVID19 accelerate this phase).