Earlier quoted context omitted.
True! But someone who learns to play the guitar, or a language at 8 ~ 15 years old shows skills that are very difficult to master (if not impossible) when you are older. There's a lot of evidence of this if you talk with guitar teachers, someone who moved and start speaking a different language when adult, etc...
Same goes for chess. 15 is already considered very late to start serious study in chess. You simply do not develop the unconscious mastery the blink like ability to play a good move instantly. It is not the lack of time in older players either. Tales abound of players of independent means dedicating themselves to chess and getting nowhere near master level. By reverse, no chess player started at 25 and made Grandmast…
Quick search turns up this list: https://www.quora.com/Is-there-any-famous-chess-player-or-gr...
Chigorin is from a different era, but he didn’t begin playing “seriously” until 24, and was a 2 time world championship challenger.
Getting to master (2200 rating) level play is ultimately just an investment of time and money. For better or worse, the “consensus” is that master level play is not due to some kind of innate ability. Drilling the pattern recognition inherent in all phases of play is the key determinant for reaching ~2200 rating. Do a cursory Google search, and you’ll turn up hundreds of threads about this topic.
Becoming an international master (IM) or grandmaster (GM) requires navigating FIDE’s, the world’s chess governing body’s, arcane rules around norms, or results, for the GM or IM title. I’m by no means an expert on the scientific piece of this, but I’d posit that the number of adults who have the financial means and time to travel across the United States or world to find tournaments that will earn them a norm is negligible.
When you’re young and your parents are paying the bills, chess can seem fun and rewarding. When it’s you personally who is paying the bills for tournament registration, hotels, and planes, it’s a lot less fun.