I have a 2005 red Cavalier that is starting to rust. Should I have it painted now or wait a couple of years.

The sooner the better.

At bare minimum remove the rust and prime. To paint or not to paint is up to you. But you should definitely do something to stop the progression of rust.

Why would you wait till the rust is so bad it needs more body work?

How long do you plan to keep the car ?