There's skepticism because age-grading is massively (understatement) flawed. Age is not the sole factor in why people get slower. There is the fact that running is less of a priority as one ages. Factors such as added stress and responsibility in other areas (work, home, etc) increase. Training is not likely to be as good as when one was in college (and likely there would be large gaps of time without training).
Do you see any masters world records that are held by anyone that was close to a world record in their prime? Until a Bekele or a El Gerrouj type decides to focus 100% on training into their 60's, we won't really know what the body is ACTUALLY capable of. I bring this up because age-group records are the basis of age-grading:
WR for 5000m (50-55) - 14:53 = 893 seconds
WR for 5000m - 12:37 = 757 seconds (.84 of 50-55 WR)
Say a 50 year old runs 16:00 for a 5k (960 seconds). That means his time is converted to 960*.84 = 13:34
Except that his "grade" isn't based on a world-record holding athlete. It's based on a time by someone that happens to be the fastest person in that age group. I'm not trying to be down on master's athletes. I think it's great to stay competitive, but the current system of age-grading is disgraceful to T&F and a broken concept.
How broken is it? Well, when Tony Young runs 3:46 at 40 years of age, his time is graded to 3:32. Tony was a 3:42 guy in his prime. If the concept of age-grading is to see how you would stack up if you were in your prime, how is it possible to have dropped such an incredible amount off of your (theoretical) time? The answer is simple. Tony Young was more dedicated and worked harder/smarter than anyone else in that age group. My point is not to take anything away from his accomplishments, quite the opposite. Rather, I say that any other 40 year old that doesn't run within 4 seconds of their 1500 PR simply hasn't put together enough dedication and hard work and don't deserve an arbitrary multiplier to reduce their time.