"多大"用来问东西有多大，或者人有多大年纪。

"多大" is used to ask how big something is, or how old a person is.

比如问别人年龄的时候，我们常说"你今年多大了？"

For example, when asking someone's age, we often say "你今年多大了？" (How old are you this year?).