Young
Youthful
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of young? It's young.
The reading is the same as the one you learned with the kanji. Oh how nice it is to be young and to be able to remember that.
若いっていいなぁ。
It's nice to be young.
彼は若いころ、日本に留学していたことがあります。
He studied in Japan when he was young.
もう若い子のノリには付いていけません。
I can't keep up with the vibe of young people anymore.