Ripen, Mature, Ripeness, Maturity
noun, verbal noun, の adjective
To become ripe(n) is to ripen and mature.
せいじゅく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
成熟した女性の脳と成熟した男性の脳の相違点について、論文を書いています。
I’m writing a paper about the differences between the mature female brain and the mature male brain.