noun
the '30s; the thirties
Refers to the decade of a century, e.g., the 1930s. The century is usually clear from context.
彼は３０年代の音楽が好きだ。
He likes music from the '30s.
この建物は３０年代に建てられた。
This building was built in the thirties.
３０年代 is a specific decade, while 年代 alone means 'age', 'era', or 'decade' in general.
Compound of ３０ (thirty) and 年代 (decade, era).