I started to teach myself guitar at 17, and quickly realised I wanted to understand the theory too. At around 40 I decided to learn bass too. I was well aware that it was a different instrument which required a different musical approach. Initially I played with a plectrum but after a couple of years I cracked finger style, just by dogged persistence really.
For a long while I had used music notation to write down material that I was working out, so I did the same with bass. I was then thrown in the deep end when I started playing with a dance band that used 99% written charts. I’m now a reasonable sight reader!
I would say that I’m still learning, particularly when it comes to theory - every so often I stumble across something I didn’t know that I didn’t know - hats off to Adam Neely!