What age is considered to be over the hill?

"Over-the-hill" is a phrase commonly associated with the point in a person's life in which he is no longer "young," but not so far advanced in age as to be considered "old." The 40th birthday is often regarded as the point at which being "over-the-hill" begins.

Although in recent years scientists have found evidence that being "over-the-hill" begins as early as age 24, the 40th birthday has for years been the benchmark. This occasion is often celebrated whimsically, with friends and family poking fun at the newly anointed "over-the-hiller" through jokes and gag gifts that recognize this comically momentous occasion in one's life.