As was already pointed out, you should check the anode rod every few
years. This is a sacrificial anode that is there to corrode away
instead of the tank. The rate of decay of the rod depends on the
content of the water, temp, any stray electrical current, etc. If you
replace the rod before it's gone, that will extend the life of the
tank. And also, as was pointed out, the life of an electric tank is
typically a lot longer than that of a gas one.