I'm doing The Harlequin Hack Audax 110, but for a popular Sportive also occurring near here this Sunday (WhiteHorseChallenge), some stats (from their handy excel entry list on website):
Tot. entry: 519
Males: 93.5%
Female: 6.5%
Club affiliation stated: 56%
Average age: 44
Mode: 43
Most frequent name listed (I think): Andrew/Andy. 4.4% Average age 46.
(Stats may contain traces of error.)