This is delayed but going back to the claim that the shelf life of elite RB's not any less than elite DB's... Here is the average age of All Pro selections at their 1st All Pro selection, their
last all pro selection, the age they stopped being a clear starter at their position, and the age they retired or were involuntarily forced out of football:
View attachment 1546
Full details here:
https://pittsburgodelendaest.wordpress.com/2018/02/16/age-and-longevity-of-nfl-all-pros-by-position/
So, no. Cornerbacks fall off no more significant cliff than any other defensive position.