Metals don't age but they do fatigue. Fatigue is only caused by repetitive strain. Whilst aluminium does have a lower fatigue limit than steel (which has no upper limit under certain conditions), you don't have to worry about this unless your ride is a large pressurized airplane with square windows.
The reason these levers failed is because the lack of engineers at the design stage. An unfortunately placed aperture in the lever caused a stress riser from where cracks can propagate.
