彼の若さ

his youth

→ 彼
phrase Rare #33,359
his youth 若さ means youth or young age; の indicates possession, so 彼の若さ literally means “his youth.”
JA: 彼の若さを考慮して、今回は注意だけにした。
EN: Taking his young age into consideration, we only gave him a warning this time.

彼の若さを考慮に入れなければならない

We have to take his young age into consideration.

彼の若さを考慮しなければならない

We have to take his age into account.

彼の若さを考慮に入れるべきだ

We should take his youth into consideration.

君は彼の若さを考慮に入れなければならない

You have to take his young age into consideration.