ranjit To me, the age brackets look pretty accurate. Some of the things there aren't exactly correct, but those overall align with my experiences looking at learners from various age brackets. It runs counter to the notion that piano must be learned as a young child. Talent absolutely exists, and children too have likes and dislikes. But if someone 13-18 becomes very interested in piano playing and has some talent, they can definitely play at a high conservatory level or maybe even concert level. Above the age of 18 or so, it depends on the individual's specific case. I think it is very possible to learn the piano well in your 20s (I should certainly hope so!). I suspect the reason you don't see this all that much is because people tend to have other priorities at that age. 35+ in the vast majority of cases gets dicey when you're talking about playing Chopin Etudes and the rest of the virtuouso repertoire. (There are some "super-agers" who are exceptions to this but are very rare.) Overall, I agree with most of what he's saying in terms of the age brackets.
Do you have any experience with a person's natural physical "demeanor", such as them being stiff, ungraceful, clumsy, etc. as far as how it impacts the learning process? I can picture learning to be more graceful, for example, would be easier the younger you are. I'd be interested in any thoughts on this aspect.