他的朋友多大了用英语怎么说

"How old is his friend?"是问他的朋友多大了的正确表达方式。

这是一个简单的疑问句，其结构为"How + 形容词 + is + 主语 +?"。这里的形容词是"old"，代表年龄，主语是"his friend"，即"他的朋友"。

下面是一些例句:

How old is your sister? (你姐姐多大了?)
How old is that building? (那栋建筑物多少年了?)
How old were you when you graduated from high school? (你高中毕业时多大?)

另外，"How old is he/she?" 是问某人的年龄的正确表达方式。
例如：

How old is he? (他多大了?)
How old is she? (她多大了?)