It actually may not be wealth and power that make the difference here, although that would be the simple answer. Those men were also not laborers who stopped working when their physical bodies slowed down. Imagine being a farmer or blacksmith who has turned 40 years old. You probably can't read, or contribute much to society anymore. Retirement is an indicator for mortality even today, so the effect was likely just as strong back then, possibly enhanced by the inability to make alternative contributions to society.