Medieval Man, played by Ronnie Corbett, has a hard life, telling the audience that he's 23. At the time of the broadcast, Corbett was closer to 70.
The Ages of Man sketch is an homage to an older, similar skit that appeared on The Frost Report (1966) in April of 1966. As its name ("The Class Sketch") suggests, class differences are used to define three archetypes, much as historical differences do in the later sketch. Barker and Corbett play what amount to the same roles in each sketch, with John Cleese playing the upper-class character who mirrors the "Modern Man" character played by Stephen Fry in the latter sketch. Several other versions of the sketch appeared in The Two Ronnies (1971).
The special was inspired by Complete and Utter History of Britain (1969), particularly the Battle of Hastings in the style of a football match.