A mattress can still be in decent condition after 20 years, though it likely won’t feel like a brand new one. After 20 years of regular use, the mattress may have lost much of its spring and cushioning abilities, meaning that it may slump more than before and might not provide the same level of comfort or support that it once did. It is also quite common for mattresses to accumulate dust mites and other allergens over time, making them potentially harmful to those with allergies or asthma. For these reasons, many people decide to replace their mattresses after around 10-15 years of use, but if the mattress looks and feels good enough after 20 years then it is possible to continue using it.