Age estimates for heating/cooling systems?

I have a handy age chart for water heaters. Is there one for heating/cooling systems? Where can I find this info?

Please share yours.

Here’s one:

Preston’s Guide
and
Technical Reference Guide

This is the references sheets. I could not upload them. I hope it let you in without a password. Sorry if it doesn’t.

http://www.reporthost.com/refSheets.asp