youngster是否是可数名词

是可数名词。
还可以用the youth ,the yong
例：
1. "People, especially youngsters don't seem so polite these days."
”如今人们，尤其是年青人好象不那么讲礼貌了。”
2. Family means some ascription for the yong as well as the elder.
家庭无论对年轻人还是老年人都意味着某种归属.
3. This book preveils among the youth.
这本书很受年轻人的欢迎.

当然可以加.
People, especially youngsters don't seem so polite these days.

是可数名词

不能加S
young people
children
adolecent