It seems few people are objective enough when ageing, to adequately evaluate driving skills. Often the changes develop slowly, and like other demanding tasks we face, we adjust. Just like you're responsible to help your parents recognize when they should quit driving, someday your children should do the same for you. When my mom reached that point, she had every excuse, such as "I only drive in the day time" and "I don't drive in unfamiliar places". When she started hitting parked cars as she drove down her street, I knew it was time. My argument that convinced her was that that parked car could be a mother with a stroller or a family on a walk. Raleigh has a cab voucher system for elderly that provides transportation for a modest fee. Knowing that she wouldn't be giving up her independence was very important. When I took her to the DMV to exchange her license for an id, the officer asked her if she was giving her up license voluntarily or was it court ordered. She did a slow turn to me then back to him and replied "not exactly voluntary". At least she still had a sense of humor. Two months later she had a series of strokes which now requires full assisted care living. We dodged a potential disaster.
As for testing, I'm for it at any age, perhaps longer terms during younger years. Like a previous poster, I am also an airline pilot. I believe that plus motorcycle riding may help keep me on the road longer as a safe driver. I guess I'll wait and see what my daughter thinks about that down the road.