Way too many variables come into play to give a time estimate or even a shot number. I could make one today and it will last forever if stored well and shot sparingly. If I shot it every day, it would not.
Wood breaks down under use, handling, and storage. The quality of the wood, the storage conditions, the shooting conditions, the number of shots taken, the design, the skill of the bowyer, the skill of the shooter, stringing methods, shot style....all affect longevity.
My go-to osage selfbow for 6 years finally failed after many, many thousands of shot and dozens of days in the field.