Why is it necessary?
You're not likely to win that argument, & if you do, the parent won't remember it! so, why push it? I'm only half-kidding.
You have to deal with safety & happiness issues -but you do not need to emphasize inadequacy & advancing age. Aging is hard enough. Plus the elder is either competent or not; if so, leave them alone, & they'll adjust. If incompetent, admitting their limits won't help.