I seriously can't believe you've started a doping witch-hunt on a public forum on an amateur runner you've never met based on him being quick and looking ripped. Nothing better to do than making baseless accusations about some stranger?
A few points:
1) He's not the MV50 world record holder for the marathon, that's a guy called Titus Mamabolo who is a full 13 minutes quicker at 2:19. Graham Green is the joint world record holder for a combined time father-son marathon. He's 8th on the UK over 50s all time list - so a very, very good runner, but not a complete outlier.
2) He's a short and light guy - 158lbs and shorter than most people he's pictured with, hardly bodybuilder weight. Being short and with low body fat any muscle is going to make you look relatively stacked, particularly if surrounded by taller runners with tooth picks for arms.
3) He has some serious running genes. Ran 4:05 mile when he was younger. His eldest son raced for England in the 800m. His brother ran a 2:12 marathon on the way to winning team bronze in the 1993 World Marathon Cup. His younger son ran a sub 3 marathon after only 4 months of running training.
4) Having great running genes and a junior background in running but then taking a 25 year hiatus from running while still staying very fit is potentially one of the best ways of being fast in your 50s. You avoid all the wear and tear on your joints of somebody who has run all their lives, and a little bit of extra muscle can also make you more resilient to injury. In your 50s the benefits you accrue from avoiding injury and being able to train consistently are likely to outweigh the benefits of shaving off another couple of pounds from a guy who is already pretty light and clearly very low fat.
Another picture to provide context - doesn't look like he's packing a lot more muscle than his son, but due to lower body fat and more of a tan the small amount of extra muscle he does have is considerably more defined.
