Our club standards follow a similar thing and the gold standards although achieveable require a heck of a lot of work for 18-39 Males and 18-34 females. 4:15 1,500, 15:55 5k 2:39 marathon etc
Then you get older and all of sudden people who were never really close start banging in silver and gold standards all over.
I’m not saying it’s wrong but I suspect it is skewed by age grading of elites probably does follow those percentages as they are many years past their peak by mid-40’s where as those who maybe don’t start running till 20’s or later have a younger ‘running age’ so don’t start peaking till 30’s and beyond (though will never likely hit the heights of those who combined Youth with years of development). Just my two pennies anyway:)