较年轻的用英语可以说 "younger" 或 "youthful"。
"Younger" 来源于英文 young，表示年轻的，类似于中文 "年轻的"。
例句：
She is five years younger than her sister. (她比她姐姐年轻五岁。)
He is the younger of the two brothers. (他是两兄弟中较年轻的一个。)
"Youthful" 来源于英文 youth，表示青春的，类似于中文 "年轻的"。
例句：
She has a youthful appearance. (她有着年轻的外貌。)
He still has a youthful energy. (他仍然有着年轻的精力。)