Then do away with the age discrimination, and retest everyone.
As the Mother of three (almost four) teenage drivers, I can get on board with that.
Not the world's worst idea. When my family moved from Indiana to Washington State in 1969, my folks had to be retested to get driver's licenses. And my dad, although in his early 40's and of sound health, hearing and vision, had accumulated enough bad habits to actually fail the test the first time. (Mom passed, and lords it over him occasionally to this day!)
While they're at it, rather than a blanket prohibition on cell phone usage, you could develop a test for people who are able to actually use one and drive intelligently, and separate out those (who for some stupid reason feel the need to look at the damned thing) who cannot. A mark on one's license plate would distinguish the two classes of driver.