Paula,
I do not believe that there are any OOTB reports for Servers that would show the Age of the overall server. I was just looking in a reference project and did not see anything. However, this does not prevent you from creating any custom reports for Servers leveraging that Age that you've added to the Servers Master Data.
You could see some insights based on the Age of the overall server population within the CMDB data. This could show you which servers are fully depreciated. In addition to that it will give you the number of servers that could be in need of replacement or upgrades for Servers that may be out of warranty, etc. Also, looking at old OS's that may need to be upgraded to a new version, etc.
Hope this helps.
Cheers,
Ryan