How do you ask "How old is it?" When commenting on a used article for sale, how do you simply ask how old the item is?
Is &quot;它多大了?&quot; Correct?
Is &quot;它多大了?&quot; Correct?

No. This can be used to ask the age of a pet, but not a used item.
You can use, “这个东西用了多少年了？” “这个东西买了多长时间了？”