The toilet itself is very durable and won’t go bad. The porcelain part of the toilet, if intact can last over 50 years. The inside of the tank has moving parts and it is recommended to replace the lever and flapper every 5 years. The handle of the toilet is also prone to breakage but can be replaced cheaply without the need to buy a new toilet. Replace your toilet ASAP if you find cracks in the porcelain. It can lead to bacterial infestation or serious leaks. Also, watch out for frequent clogs and weak flush. These don’t mean your toilet went bad but can mean that it is inefficient and needs to be upgraded for a more modern unit. Likewise, if the toilet you own was built before 1994 or is at the point when you can’t get it clean it’s time to think about a new one. New toilets that came out after 1994 adhere to a strict water conservation policy. They have to flush using a maximum of 1.6 gallons of water. A toilet that has significant mineral buildup can be really hard to clean. If you moved into a house where the toilet wasn’t cleaned well for years, consider replacing it. You can still use it but it is not very sanitary.