It depends on the type of retaining wall and the material used. Generally, a concrete retaining wall will last around 50 years, while a timber retaining wall will only last around 15-20 years.

There is no definitive answer, as retaining walls can last anywhere from a few years to a lifetime, depending on the materials used and the care taken in their construction. A well-constructed, properly maintained retaining wall should last for many years. However, if the wall is not built correctly or is not maintained properly, it may fail prematurely. Factors that can affect how long a retaining wall lasts include the type of soil it's built on, the climate (e.g., freezing and thawing), and exposure to water or other elements.