As Viaggiatore says, in romance languages we don't say: "I am X years old". We "have" years, and so "Io ho 20 anni" (it), "tengo 20 años" (es), "tenho 20 anos" (pt), "j'ai 20 ans" (French), "eu am 20 de ani" (ro), etc :D
What would "He is older or younger than me" be in Italian? (though I know it's meaningless! I just wanna know if we use ESSERE is this case or not.)
Shouldn't it be in english: "he has more or less my age" and "he is more or less as old as i am" and "he is more or less of my age"? "He is my age" seems unnatural to my (non-native) ear.
I'm not an English native either, and I did prefer "He is more or less of my age", until a native said it's a bit old English, and "He is my age" is already OK. Plus, I don't think they use "have xxx age" in English, judging by how confuse they are when they first saw the structure "ha...anno" in Italian and Spanish lol.
Why can't you say "It is more or less my age" (for example if one was guessing your age).