it's normal that dull's percentage is higher than rogers, because he's a early bloomer. he won his first slam 19 years old at his 6th slam-appearance. fed was almost 22 years old when he won wimbledon 2003, it was his 17th slam-appearance.
as slade said, the percentage will decrease with higher age.
percentage since they won their 1st slam:
dull 13/37 = 35,14%
fed 17/42 = 40,48%