how many (used to ask about quantity or number)
りんごはいくつありますか？
How many apples are there?
クラスにいくつ机がありますか？
How many desks are in the class?
この箱に入る本はいくつくらいですか？
About how many books will fit in this box?
how old (used to ask someone's age)
お子さんはいくつですか？
How old is your child?
その猫はいくつなの？
How old is that cat?
彼はいくつで大学を卒業したのか覚えていない。
I don't remember how old he was when he graduated from university.