To find out the age of the heater, find the serial number, then contact manufacturer, Lorenzo has a search engine in the top left corner of this page it is useful for this kind of stuff. Manufacturer can tell you year month and some even the day of manufacturer. Also most have been good about replacing defective diptubes, supplying new diptubes installed by a plumber. But is the diptube the problem. Well if you are getting little white pieces of plastic building up in your aerators on your faucets reducing water flow. And you used to be able to have long hot showers but now you dont have time to get soap in your eyes much less out before you run out of hot water, then your diptube could be the problem. Below is a link to a page with more info on your problem…..Lou