Hello Nicque

To login on web manager  page of modem follow the below link :

http://arris.force.com/consumers/articles/General_FAQs/SB6183-Cable-Signal-Levels 

In the web manager page we cant see how old the modem is, but it can show you status/product information/ event log and etc.,

To check how old  the modem is  , we can only calculate the warranty of the modem from the date of purchase its 2 years of warranty is provided for all the modems/gateways purchased from Arris. 

Let us know if this helps .