Drain Pipe Question

I am in the process of replacing bathroom lavatory faucets and will be installing new shut-off valves and supply lines. I am also considering replacing the drain pipes. The currect drain pipes are metal.

1. Is it a good idea to replace the current drain pipes? They are 22 years old, but are not leaking.
2. How does one determine if they should use metal or PVC drain pipes?
3. Can metal and PVC drain pipes be intermingled?

Thanks,
Bertman48

What kind of "metal"? Cast iron, copper, or galvanized? If CI or copper, leave it alone. Galvanized may be getting rusted and corroded.

While you are at it, squeeze the bottom of the trap. If it is chrome plated, and somebody used drain cleaning chemicals, sometimes the only thing holding it together is the chrome. It can last a very long time if not abused.