I believe in a fundamental rule in the long term development of athletes. I see it broken all the time, across teams at all levels. I believe athletes ought to choose their sport, but oftentimes are never given that choice.
Sports in most of the world are voluntary, at least in theory. There is no legal requirement placed on Americans, for instance, to come out for the football team. In practice, many kids are pushed into sports at a young age by well meaning parents who want the best for their kids.
As a parent, I know that you won't always get your kid to do what's best for them voluntarily. My daughter doesn't always want to go to sleep when she's really tired. You get used to overriding young kids a bit for their own protection.
Unfortunately, too many times it crosses a line. Too many young kids in swimming are being trained without their consent. They are compelled to come to practice by parents, and compelled to do things in practice by coaches.
This is a broken model- at young ages, the most important measures you should use are whether kids are enjoying the sport, and learning skills (technique) that will help them down the line.
I talked with a friend recently who told me about being a nationally ranked age group swimmer at age 10. I was expecting to year about the slog of training that he went through. To my surprise, he said that he was only practicing three times a week at that age. The primary focus of every practice, as he recalled it, was playing some games and learning a bit of technique.
This is an environment where an athlete can grow up to make a choice. As with all developmental steps, they will be ready at different ages. Some will be there by around age 14 or so, some even older. This is the age when a swimmer can finally decide for themselves "I choose swimming".
This is when they can choose to do it year round and forego other sports. This is when they can choose to do double practices and push their limits. This is when they can start to put pressure on themselves to perform.
If they aren't given the choice, sooner or later they will wake up one day that they have been putting a lot of time into something that they didn't choose. They may not quit the sport that day, but their mind won't be able to quiet the voice that reminds them of this.
Sadly, there have been countless Olympic medalists who never got the choice. Their success is held up as a reason to keep pushing young swimmers before they are ready. This is wrong- and those swimmers while going extremely fast are worse off in life for never being given that simple choice.