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(one's) 30s; thirties
三十さんじゅう代だいで家いえを買っかった。
I bought a house in my thirties.
彼かれは三十さんじゅう代だいの男性だんせいだ。
He is a man in his thirties.
彼女かのじょはまだ三十さんじゅう代だいなのに成功せいこうした。
She succeeded even though she is still in her thirties.