In my experience, children who excersise a lot become adults who have a far better baseline and exercise comes easier. Children who never do anything become adults for whom excersise is much more difficult. This seems in line with what the article says about learning?

It slows aging, not reverses it. If the first time you learn 4 languages or get into exercise is when you are 70, you don't immediately have the mine and body of a 57 year old

> This seems in line with what the article says about learning?

No?

Children who learn multiple languages don't necessarily become adults who continue to learn more languages beyond what they learned in childhood, so the analogy with exercise seems to break down.

Children learn the languages that are spoken around them. If it's one language, they learn one, if two or three, they learn two or three. This happens naturally, for all children, regardless of personal habits.