The only way you may have of estimating the life expectancy of your water heater is by going by what is the norm for your area. In my old home town a water heater has a life expectancy of five years, where I live now I have replaced some that are thirty years old. If you do not have a tank pan with drain installed under the tank, and you are worried about big time water damage, then it might be a good idea to replace the tank soon and if it doesnt have a tank pan and drain under it get one installed at the same time. This will give you peace of mind, a stitch in time will save you nine…Lou