Over the hill

[Mark Zuckerberg]

Meaning that you are 40yrs old, therfore you have reached the climax of your life time and your beggining to go over the hill.

[Britney]

Reaching the average mid-point in life, which is age 40. Therefore 40th birthdays are generally thought of as making it over the hill. Youve gone up the hill for 40 years ⬆️ (healthy, youthful appearance, etc.), now 40 more years down the hill ⬇️ (decreasing health, loss of physical beauty, etc.)

[Sarah]

A mature person over the age of 30.

[Luis Fok]

In the rest of the world over the hill refers to someone over 40 or 50 but in Birkenhead your considered past it if you arent married with kids at 19.

[Rihanna]

when you are 50-yrs-old and to old to live...
heh....

[PussyCat]

used for describing someone who is old and no longer useful or attractive