アラフォー (Arafo) is a new Japanese word. It was familiarized last year and is a vogue-word. It is used for women who are around forty years old. I think that Japanese are concerned about actual age, especially for women age. For example, we often say that she looks very young or old as compared with her actual age. We regard being young as an advantage or privilege in our society.
However, アラフォー isn't negative word. Japanese women who is Arafo are very active in our society now. For example, a tennis player, Kimiko Date who is Arafo generation, came back as a pro tennis player now. She entered Australian open tournament this month. (She unfortunately lost.) Everyone was surprised at her comeback at first. However, she has won some tournaments in Japan and we praise for her powerful performance.
We tend to think that getting old is very negative thing. However, everyone gets old. Women should live actively anytime without being afraid of getting old. "アラフォー" is a word that encourages every women.