Why platform life is more than age

Do people underestimate why ships, aircraft, and helicopters eventually need replacement?

Often. Age is only one factor; operating intensity, upgrades, maintenance, and mission demands are equally important.

The comparison of Type 45, B-52, F-14, and early F/A-18s separates engineering life from service value. A platform can remain physically operable yet become too expensive to update for the mission its owner demands. Salt water, high-performance operations, and the cost of modernising complex systems all shorten useful life. Deferred maintenance also reduces fleet availability because heavily used ships eventually need long periods in the yard.