Water heaters in general are reliable for around 10 years. They can last much longer or they can start to fail after 5 or 6. (the oldest I have seen was a 68 year old electric water heater that was still cranking away!) Among other issues with water heaters, the age is a good indicator of when the unit may start to fail or when you may need to replace the unit.
The thing I look at, when I am inspecting homes in Salem, Oregon and the water heater is the name plate:
The name plate will give most all of the information we need to determine the size and age of the unit. Some times the age is very obvious and there will actually be a label that states when the unit was manufactured. Most of the time you have to look in to the Serial Number. With most brands the year will be the second 2 numbers in the serial number.
At this point I am tired of talking about have concluded some brief ideas on what to look for when looking at these super stylish modern appliances. You can check out my earlier posts here: More water heater information
Jim Allhiser President/Inspector