The only differences between you and most people over the age of fifty is that you are being honest with yourself and you are responsible and ethical enough to look to alternatives. While there may be an organic cause to your decline, noticeable declines are the norm, not the exception. Sure go see your physician, but don't expect her to find anything out of the ordinary.

It's a pity more people don't assign a younger person to evaluate their driving on a regular basis and tell them when their decline indicates "It's time..." You can't notice what you can't see, kind of by definition.