It was so much easier for DD when 3 to jump into the deep end of the pool than for an older child.
Ah, but my kid was terrified of the water at 3, despite having been in swimming lessons since ~18 months. And every time she went in the pool, it got worse. So we did nothing until she was 7, and she decided she wanted to swim, and by the end of her first lesson, she could swim (to some extent) - and could jump into the deep end.
I was a shy kid who never wanted to speak in front of anyone (and ran away from dance recital in tears) until I was in high school, and competitive speech class was the lesser of all evils in offered electives. And I liked the preparation enough that I sucked it up and dealt with the "in front of people" part, and I was good at it.
It is not categorically easier to do something scary when you're younger, than when you're older. It's easier to do something scary when you want to do it, than when you don't want to do it.
