Not any structural engineers here?
A ski can be used up by repeated tunings, this is normal and expected.
Composite structures lose their design parameters through overstress, low cycle fatigue, high cycle fatigue and material aging of components.
Overstress is a one off event usually due to an accident. You can bend a ski.
Low cycle fatigue is repeated near overstress that causes structure failure usually because one of the component layers is repeatedly stressed to failure. (eg: some foam plastic cores).
High cycle fatigue is true wearing out. It is due to the accumulation of microscopic damage to component layers or adhesive. This shouldn't be an issue with most skis but is a big issue with things like aluminum airplane parts.
Aging of component layers and adhesives is mostly a design and build quality issue. A well made ski with a high quality wood core that is stored properly shouldn't have issues with aging. Some of my well made wood core skis that are 30 yo are still in good shape.
Most strong skiers want a ski that is pretty flexible for their weight/power. They run their equipment pretty close to the overstress condition and will "wear out" a set of skis quite quickly where low cycle fatigue causes a change of structural shape. Most of us know a beast that can destroy a set of off the shelf skis in a day or a run. This is an issue of improper equipment and not wearing out.
A reasonably good skier who doesn't overstress their equipment and stores it properly can expect a very long life from high quality skis.
If they don't get it the skis were not designed or built correctly in the first place.
High level racing, bumps and big air require skis constructed to take this abuse.
Ski construction cost is limited and sometimes, if you want them bendy enough to work well, they will eventually fail.
Then there are some like the P40 Volkls with three sheets of titanal that could be used as bridge parts and will never fail when skied by mortals.