Wanking article.

I've known several (relatively) late-blooming competitive swimmers who didn't begin training until their teenage years, and a few other athletes who began later than that (20s, 30s, and beyond), reaching national or international class.

Gail Roper comes to mind. She was largely passed over for swimming in high school, but came to be one of the most dominant masters and open-water swimmers of all time. A few decades back I had the distinct pleasure of being beat by over 4 minutes by her, which I figured was fine given that she had a 40 year head start.
http://www.girlscantwhat.com/meet-gail-roper-the-most-domina...

The "you can do anything" mentality is, of course, false on its face. Athletes, entrepreneurs, and artists, when confronted with a microphone shoved into their face, will say whatever damned fool thing pops into their head, sometimes honestly, often not. If you want to know the real secrets to their success, look at what they do, not what they say.

And yes, Phelps is a genetic freak pretty much uniquely suited to swimming.

He's also just another human being. And at the end of a race, his muscles and lungs are burning just like anyone else's would be.

That said, the accomplishment domain most of us are competing in is "doing stuff", surrounded by others trying to do the same thing. If you want to become accomplished at something, then a mix of innate ability, talent, and hard work will push you somewhere toward the envelope. Perhaps well inside, perhaps outside.

A huge part of success, beyond what you can't control (your genes, circumstances, starting at age 7) is to practice efficiency in how you go about reaching your goal. As many hours as a person puts into pursuing a given goal, there are far more hours spent not pursing it. In the tech world, most of us come to realize that beyond a few hours a day, if we're lucky, we're not terribly productive.

Athletes may spend a few hours a day engaged in training, but the real pay-off moments may be a few minutes of Tabata intervals, or a set or two of max-effort lifts. Everything else is preparation, support, preventive measures, recovery, or just plain goofing around. What's impressive is how little of the right effort is required to improve your ability. Perhaps not win you a gold medal, but at least to nudge you in that direction.

In another context I saw yet another question of the form "how much can I expect to progress if I do X?", and saw the usual responses, some backed with links to substantial research, of what typical and outstanding progress might be. One response came close to what I realized was the right answer: "and if you don't hit some goal rate of progress, are you going to quit?".

The answer is: you'll make more progress than if you don't do X.

So: pick a reasonable goal, within the realms of physics and biological attainability. Find out if it really suits you (are you doing this for you, for for someone else). Find effective means of attaining your goal. Apply those methods. Monitor your progress. You may find you are able to go further. You may find the goal is out of reach. You may find the goal doesn't interest you.

But you tried, and you learned something.