Oh, That 40

Perusing a list of popular Japanese words and phrases (HT, MR) I come upon:

14. Arafo (アラフォー): “Arafo” — a word coined to refer to females between the ages of 35 to 45 — is an abbreviation of “Around 40,” which also happens to be the title of a popular TV drama that depicts the worries and conflicts of the Arafo generation, particularly with respect to career, love, marriage, childbirth and child rearing.

And here I thought it was waist size...