Help with age of Lennox unit.

I was doing my typical “Open House” Sunday tour looking to drum up business when a real estate agent ask if I knew the age of the heating system. It is a Lennox oil fired steam unit, not too old. The plate had model #CDB-E3.7, but I could not find a serial#. The basement was dark and I did not bring my flash light. This is an agent I have not worked for before and I would like to dazzel her. Please help.
Tom Pszczolkowski
NACHI member 02120206
PS… Having trouble getting into the member only section…please help