Translation:It is six years old.
Can this expression be used with inanimate objects, such as a building or a business?
In traditional chinese, we still write "ta" to make the distinction :
The simplified Chinese only uses 它
Actually, 牠，它 and 祂 can all be used in Simplified Chinese, they're all still ㄊㄚ/Tā (I double checked on my keyboard) but it's kind of like 妳，it can be used in both but Chinese people prefer to just use “你”
Is 岁 a classifier? 它 seems to be a pronoun and 六 a numeral, if such classifications exist in Chinese.
They do, although since I'm a student of the American system, I don't know what a classifier is, although 岁 means "years old"
Because that would be saying that they are "a six year old" as if you're an object called "six years old" Like if you said "我是一隻貓” (I am a cat) you would be saying that you are physically a cat. Sorry, my explination is bad but I tried. I hope that helps.
Essentially it's just a difference between English and Chinese. There's no real explanation other than they're just different languages with different rules.
English: "I am 6 years old" French: "I have 6 years" Chinese: "I six years old"
There's no way other than to pay attention to the context. All three have the exact same pronounciation.
I wouldn't worry too much. It's rarely important in conversations.