A wood window is not one product with one lifespan. It is an assembly of components on very different clocks, and understanding those clocks makes maintenance predictable rather than reactive.
Insulated glass seals are typically the shortest-lived component, with service lives commonly measured in fifteen to twenty-five years depending on exposure and unit quality. Weatherstripping is shorter still — a wear item measured in years. Hardware follows cycle count, not calendar age.
Finish systems on exterior wood require renewal every seven to ten years on protected elevations, and considerably sooner on weather-facing ones. Deferred refinishing is the leading cause of the decay that later gets described as the window having failed.
The wood itself, kept dry and coated, outlasts everything else in the assembly by a wide margin. Frames a century old are routinely sound where the finish schedule was maintained. That asymmetry — a long-lived substrate carrying short-lived components — is precisely the argument for restoration.