The usage life of watch still could not be express in an exact number. It is related to the wearer.
A good watch still can work normally after decades if maintained properly.
High-end watch should be maintained in every two years to replace the waterproof components, test working function and movement power, maintain movement and clean appearance.
It is good to put some desiccant on the place where putting watches, but paying attention to avoid the use of camphor pills, insecticides and other chemicals.
Watches can not be used in the strong magnetic field environment. It also should not be worn when swimming, even for the watches that marked waterproof.
Usually do not wear the same watch every day, you can prepare several different watches as alternate. In this case, you not only have different style and appearance every day, but also avoid dust on the same watch.
All in all, treat the watches as your friend in your daily life and protect it carefully. And your watches will have a long long life.