A generation is considered 25 to 30 years. So relook at your math.
And every component of a mechanical watch can be replaced or manufactured if the part is no longer available by the watch company.
On your definition of 25-30 years, the Apple Watch will not be functional and terribly outdated to the point of being worthless/unusable. And you are right to point out how each component of a mechanical watch can be replaced. Not so with an Apple Watch.