I was self taught by 10. My Mother still insisted I take a beginners swim class at the high school. There were 3 of us that already could swim. After the class they had free swim time, and we're diving at the deep end, etc. Instructor was like wtf. Needless to say, I passed and got a little card stating I knew how to swim which satisfied my parents.
I don't get much swimming in nowadays. I'd need to join a gym, or I think the local HS has open swim on Saturdays. In the summer could go to one of the local lakes.