Hulk Hogan's memorable encounter with The Rock at Wrestlemania X-8 took place while Hogan was about 48.5 years old. Meanwhile, the future of the "Wrestlemania Streak" is in flux as a 48 year-old Undertaker may not be able to perform at the 2013 Wrestlemania. Here is a comparison of those men's career's by age:
Hulk Hogan (matches by month)
(Results in the 1980's are spotty)
The Undertaker (matches by month)
So, early 80's records aside, it's pretty clear that UT wrestled probably more 30% per year versus Hogan at the same age over the past 14 years, and prior to that Taker was working a lot more than Hogan, but I feel that is partially due to incomplete record-keeping for Hogan's beginnings. Also, this is looking at matches versus just appearances (which Hogan would certainly beat UT at).
The biggest number for me is Hogan in WCW was working less than 200 matches total from 1994 to 2000 (he was 40 to 46 years old at that time). At that same age (40 years old to 46 years old) Undertaker worked twice as much (more than 430 matches from 2005-2011).
I feel that not just number of matches, but the age at which you continued to accumulate them. (Not to mention the style that Undertaker worked and the style that Hogan worked. Or, I guess "to mention" it. Because I just did.)