Say I have an old friend. We have not seen each other for about 10 years and we met on a street while passing by the street(=>by the way, can I omit "the street" in "passing by the street"?).

Do I say, "Wow, I haven't seen you for ages"?

If so, is there also other expressions like "I meet you again for the first time for 10 years?"

Thanks in advance.
Hello VC

Yes, that's fine.

For your 2nd question, maybe: 'How long is it since we saw each other? It must be at least 10 years!'

But your first is better.

(Yes, leave out the 'passing by the street'.)

'Passing by the street' makes no sense unless we know WHICH street you are referring to. Did you mean 'passing by IN the street'? That has a different meaning.

and, a suggestion:

"It must be ten years since last we met!"