Ah, it seems that most many wind turbines have a design lifetime of 20 years.
I guess that living in a country with many wind mills that are hundreds of years old, made me assume that a wind turbine would also have a technical life of more than two decades.
Depends on what you want the wind mill to do for you: slow and steady pumping water up a dike exerts somewhat less force on all the materials than trying to maximize electric output you get out of each rotation.
Also, there's no several 100% efficiency increase in upgrading a wind mill, so the parts are probably still compatible...
If you feel a whole wind mill like this one https://en.wikipedia.org/wiki/De_Gekroonde_Poelenburg
shake when it is in operation, then that is very far from a slow and steady operation. In fact, most wind turbines feel far more 'slow and steady'. This one is not very old, only 150 years.
I assumed that with a 20 year old wind turbine, the money you make from the electricity it produces would be more than maintainance costs. Even if better turbines exist, if you can't build a new one in the same place, it might make sense to keep it running.
Of course, if the maintainance costs are indeed high enough that you don't make any money, then it make sense to take it down.
I guess that living in a country with many wind mills that are hundreds of years old, made me assume that a wind turbine would also have a technical life of more than two decades.