One page, two tops
If you can't condense your resume down to one page, two at the most or you aren't doing it right. There is no need to list all of your previous employers, especially if they aren't relevant to the current position. Nobody cares that 25 years ago you worked for McDonalds. Similarly, no one cares that you did thee projects in COBOL 20 years ago.
The point of a resume is to highlight what you know and have done that is RELEVANT to the position they are looking to fill. It also allows you to highlight past experiences. It is not a complete life history, or even an exhaustive work history.