年代(nián dài) - era, period, age; decade in Mandarin

年代 (nián dài) does two jobs. Loosely it means an era or period, the stretch of years that had its own character. Precisely it names a decade, and this is where learners get caught out.

To say a decade you give the year with the tens digit and add 年代: 八十年代 is the eighties, 九十年代 the nineties. For a century you put it in front: 二十世纪八十年代 (the 1980s), 二零二零年代 (the 2020s). English drops the century; Mandarin usually keeps it in writing.

Do not confuse it with 时代 (shí dài), which is a named age defined by what happened in it: 信息时代 (the information age), 唐朝时代. 年代 is measured in years, 时代 in significance.