Example of write up if you can not find sufficient supporting documents of age:
Keystone water heater - Crane. Serial# 2393660 We were unable to find supporting documentation to verify date of manufacture. Water heaters have a life expectancy of 9-15 years that generally can be extended with proper care along with manufactures maintenance suggestions but depending on use and water condition or makeup. Due to the vintage look of this unit, we anticipate it to be over 25 years. Budgeting for repairs or replacement should be anticipated.