A low flush toilet is a porcelain unit with a detachable seat and working parts in the tank. The working parts in the tank are normally made of metal and plastic. There are also feed pipes that run from the wall pipes to the tank, and the wax seal that prevents the toilet from leaking all over the floor.
The parts with the shortest lifespan are the working parts inside the tank. Once those parts start going bad, it is best to replace them, but that can take upwards of 15 years. The wax seal could last for more than 30 years so long as the toilet is not moved and the seal is not broken. The feed pipes should be changed when they get rusted, which can also take 15 years or more. The porcelain toilet itself can last well beyond the average human lifetime.