Three years ago I started swimming after back surgery for a low impact aerobic activity. When I was young, I swam around lakes and pools but never on a swim team and was never coached.
After several months of swimming on my own, I joined a US Masters swim team. The US Masters Swimming is a terrific way to learn swimming or get back into it. It is a coached practice for all levels of ability. They divide you into lanes based on your ability. As you progress, you move "up a lane." I started in lane one and watched in amazement at some of the swimmers in the "fast lane." They were former college swimmers, a former professional triathlete, and people who had worked their way up and were just plain fast.