～代

A number that's a multiple of 10 + 代 can be used to describe someone's age, with 20代 meaning 20's, 30代 meaning 30's, etc. If it's used with a year in the format of 1950年代, then it's referring to the 1950s.

私は10代で結婚してすぐ子供を産み、40代で孫が産まれ、「おばあさん」になりました。
I got married in my teens and soon had a child, and in my 40's my grandchild was born, and I became a grandmother.

20代でリーさんに会ったんだけど、30代で付き合い始めたんだ。
I met Lee-san in my 20's, but I started dating him in my 30's.

1980年代の後半から1990年代の初めにかけての日本の経済は「バブル経済」と呼ばれている。
The soaring Japanese economy from the second half of the 1980s to the early 1990s is known as a "bubble economy."

彼は２０代で会社を作り、３０代で、大金持ちになった。
He started a company in his 20's and became rich in his 30's.