youngster; neophyte; greenhorn
若僧のくせに、口出しするな！
You're just a greenhorn, don't butt in!
この若僧に、大役が務まるものか。
How could this greenhorn possibly handle such an important role?
ベテラン社員から若僧扱いされるのが不満だった。
I was frustrated at being treated like a youngster by the veteran employees.