Noun. The surprising and previously unknown discovery that one experiences when it becomes clear that older women are in fact fitter and more desirable than younger women.
Patient: "I don't know what to do, doctor. I'm married to a wonderful woman, I've got a great sex life, but every time I see 45 year old Brenda at the office, I get chest pains and need to go to the toilet."
Doctor: "Oh, that's nothing too serious, normal for a chap in his twenties like you. You've obviously had a recent milfelation. Here's a prescription for '40 and Over 40', drop it in at the Fags 'n' Mags shop and you'll be back to normal before you can say ‘Women's Weekly.’"