Age grading is better for going forward than back. So if you look at a time at age 40 that you were running for the mile and then compare it to an age graded mark at age 50 maybe you can get an idea if you are actually doing better in some way compared to your own personal athletically ability. It really doesn't matter. What is cool is that there are great runners breaking the age records and gives upcoming runners something to shoot for. Pretty good time for a 55 year old. Given 10 years this may be 4:29. I am sure a 45 year old who is capable of a 4:15-18 mile may be able to run a sub 4:30, if they stay healthy, just so many factors, who knows.
The real benefit is how incredibly fit these guys are and how they must feel compared to your average 55 year old. Amazing and inspiring.