I will not argue with physical fields (like gymnastics)
However, the lack of chess GMs who started at 25 could be explained with very few 25 year olds attempting to become a GM starting at this age.
At this age, capable people are busy with their lives and I suspect overwhelmingly will not even attempt reaching grand mastery in chess.
To settle this scientifically we would need to find a group of 25 year olds who never practiced chess before and do 5-7 years of study (the same level of intensity that your 13yo grand masters perform).
I wouldn't be surprised if the set of such people is empty.
A thing we would need to control for is natural aptitude (perhaps IQ would be applicable here?). So we should take our 25 year olds and compare them to a group of kids with IQ in the same range who are going through similar study regimen.
Here, we may find that the 7 year olds who attempt and complete rigorous study chess are all mental prodigies to begin with and it will be even harder to find comparable 25 year old group.
At this age, capable people are busy with their lives and I suspect overwhelmingly will not even attempt reaching grand mastery in chess.
To settle this scientifically we would need to find a group of 25 year olds who never practiced chess before and do 5-7 years of study (the same level of intensity that your 13yo grand masters perform).
I wouldn't be surprised if the set of such people is empty.
A thing we would need to control for is natural aptitude (perhaps IQ would be applicable here?). So we should take our 25 year olds and compare them to a group of kids with IQ in the same range who are going through similar study regimen.
Here, we may find that the 7 year olds who attempt and complete rigorous study chess are all mental prodigies to begin with and it will be even harder to find comparable 25 year old group.