If you built the home or installed the heater when it was new, then you might know the answer right away. If you purchased the home from a previous owner and you don’t have any history on when the water heater was last serviced or replaced then you can find out it’s age by locating the serial number on the manufacturers sticker and contacting them. You can also decipher the serial number yourself if you know how to read the serial numbers.
Your serial number might look like “D079467322” The first letter (in this case “D”) is the 4th letter in the alphabet and represents the 4th month in a Calendar year. In this case March. The next two numbers indicate the year. In this case it’s “07”, the water heater was made in March, 2007. Most manufacturers are following a similar format for their date of manufacture as well.