I was taught by my driving instructor to speed up when we left the 30mph limit. He told me I would fail my test if I didn’t. My Mother-in-law was pulled over by the police for driving too slowly.
But I worry more about drivers who go too fast, who brake too late, who don’t signal, who overtake dangerously.
As for older drivers, yes, a specific retest would not hurt. If not at 70, then 75 , 80, then every two years. I know we all age at different rates but most of us restrict ourselves to roads we know. I would not drive in a strange city, but am happy to drive to places I know, including on motorways. My least favourite place is a supermarket car park!