We should never have let it get this far. Computers have been around for 50 years, nobody in the work force today should have thought that they could avoid them.
So yes, after getting 50 year olds to sit down and mess around with a computer for a couple months to see if they can "get" it, they should be let go. We fundamentally hire people to do a job. When they can't effectively utilize technology they are holding back society. It would be better to put them on welfare or to have them transition to a lower tech position. I don't want the local police chief installing some browser spamware and having all the juvie records leaked.
Personal computers came later. I remember in the mid nineties when I was in my teens and bought my first PC. I was one of the few people in the village to have a PC.
I imagine that people in their 40's and above got acquainted with computers in office settings when they were already adult. Adult non-geeks can be very resistant to change, especially repeated one.
Even if 50 year olds don't "get it", they have something that 20-35 year olds don't -- power and influence within their organizations.