>>43334794Varies wildly depending the men involved, the place, and the time period.
Skill and experience matter for a hell of a lot in a fight. If the old man wasn't riddled with arthritis or gout and was a veteran, then he could hold his own. Mind you that the level of average fitness for most previous ages was much higher than the modern norm, especially for fighters.
For the medieval period in the west, retirement didn't exist, per se. You wouldn't likely be called to service if people knew you were too old to be of use, but the bonds of fealty and vassalage were forever. A landed knight might spend his old age at home in his estate, but generally, service was until death.
Childhood existed, carefree childhood did not. For the poor, work was expected, and for the noble and well-off, education was applied. I think, among noble and near-noble circles, being a Page started at 8 and a Squire at 14.