If you get recurrent kidney infections, how long would it take for kidney damage/scarring to develop? i.e is it months or years?

Each kidney is made of 1 million of nephrons. When the infection is severely enough, many nephrons will be destroyed and they can't regenerate. However, the remained nephrons can work harder to compensate for the losses and those nephrons will in turn get old faster and die earlier than their true life span. So, damage is right away but you do not know recognize it until many years later.