Which is better:
He is three years older than me.
He is three years as old as me.
He is three years as old as me is an absurd sentence. It doesn't make any sense. If I break your this sentence ' he is three years as old as me' in two sentences , we will say HE IS AS OLD AS ME,, meaning we two are of the same age. I am 23 and so he. Similarly , he is three means he is three years old.
So keeping these two sentences together , one from HE IS AS OLD AS ME and HE IS THREE and making it one , doesnt make any sense.
He is three as old as me., here you are not comparing your age with the other person.
I am not a teacher but hopefully have tried to make you understand the meaning of the above mentioned two sentences.
Thank you, Roselin. I don't know how it occurred to me to ask such a stupid question. Must be overworked.