Otherwise all the best footballers would save themselves until they'd paved their way to learning how to play by baking cookies and taking pride in it.
Or violinists. Or opera singers. Or mathematical prodigies. Or chess players. Or engineers.
But still. Some of the best people I know when it comes to making up algorithms for cutting edge problems, had definitely reached their adult height when they first learned what a compiler was.
(I will grant I don't know any really good programmer who started coding at e.g., 40. But there are relatively few people who change careers at 40, so my sample size is very small. )
I also suspect that if you flex those particular muscles hard from a relatively early age, they will become stronger relative to someone who doesn't. The original author believes that programming requires a unique combination of skills/abilities which is why he is fond of it. If that's genuinely the case you're better off starting practicing that earlier than later, surely?