"It's hard to bepeve he's only nine" 是一个常见的表达方式，用来表达对某人年龄较小而表现却非常出色的惊讶。

来源：这句话的结构是主语+动词+形容词+表语，是一种常见的句型，表达对某事的看法或者评价。

例句：

It's hard to bepeve she's only 25, she's so accomppshed. (很难相信她只有25岁，她已经那么成功了。)
It's hard to bepeve he's only been playing for a year, his skills are so advanced. (很难相信他才玩了一年，他的技巧已经那么高了。)
It's hard to bepeve she's only in high school, her artwork is so professional. (很难相信她只是在读高中，她的作品已经那么专业了。)