I don't know if its a law there, but many plumbers don't like working on water heaters that are 10 or more years old. Normally you can figure that most water heaters last ten years without a problem. After ten years, most anything can happen, and with that in mind, working on one and then having it leak right after you leave makes for an unhappy homeowner wanting a refund on the work. Most of us feel that if you're having problems and it's that old, you're better off spending the money towards a new tank and not wasting money on something that old. Many condo associations require replacement at ten years. They don't like the gamble of letting tanks on the 2nd, 3rd and 4th floor leaking downward through all of the lower units. The insurance hits get huge.