What to do about Near Miss, Elderly Missiles....

After being almost run off the road, ran into in the parking lot, and almost turned into while driving a straight road today, I have to ask....  Why are the old allowed to keep their driver’s licences long past the time they need to be revoked?

Many people joke about this subject when driving, some joke about it seriously, but nothing is ever done about it.  Admittedly, they should still be allowed to drive if they CAN drive, but there should be mandatory testing, or something, after a certain age.