He doesn't look a young man in his ______(thirty)

He doesn't look a young man in his ______(thirty)
He doesn't look a young man in his ______(thirty)

He doesn't look a young man in his ______(thirty)
thirties

答案应为：thirties
学过的一个词组：in one's +数字的复数形式

答案：in his thirty
意思是在某人三十的时候
in one's age 表示在某人多少岁时
那个
thirty thirties都可以
前者表示在他三十岁时，后者表示在他三十多岁时