Not Yet Good At
Not Good At
noun, な adjective, の adjective
Not yet ripened, means you haven't really come into form yet. It means you're not yet good at something.
みじゅく
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
俺も昔は未熟で好き勝手してたよ。
I used to be immature and I did whatever I wanted too.