For a road bike used by a recreational cyclist, what is the life expectancy of cable housings for shifter cables, either in terms of miles or time?

I ride throughout the year. I don't ride in snow or ice conditions and do not ride in the rain unless it starts raining during a ride.

I have two road bikes, one with 12,500 miles and the other with 14,000 miles. I've changed cables as needed but not housings. The bikes are kept inside my dwelling when not in use.