A septic system typically lasts between 15 and 40 years. This is usually determined by the quality of the tank and the drain field. A concrete tank is extremely durable. When constructed well, it is fairly indestructible and can easily last 40 years. The lifespan of a plastic tank is about 30 years. The drain field can also be a limiting factor on the age of the system. The drain field type does not affect the lifespan of the system. However, the quality of the soil and drainage is a huge factor. Not doing maintenance on the system is one way to shorten the life of any system.