"Engels had asthma as a youngster and doctors told him he should not participate in sports. But he decided to overcome his ailment and ran his first marathon at 25. He said his latest feat is the result of 35 years of exercise."
Christopher McDougall, in his book "Born to Run" and in various talks, tells us that humans maintain their endurance until a surprising age. A 49 year old has the endurance of an 18 year old.
