Abstract: The present invention providing a control and method having for starting and stopping gas turbine engines in a set of such engines controlled from a master controller. Incorporated in the master controller is a predetermined optimum life schedule selected to make maintenance intervals predictable. The actual age of each engine is compared to its optimum age as determined by the schedule. When power demand increases, the master controller will always start the engine whose actual age is the farthest below its optimum age and when power demand decreases, the master controller will always stop the engine whose actual age is the farthest above its optimum age. Thus, over the life of the site, the aging of the engines will converge on the predetermined optimum life schedule making maintenance intervals predictable.