Well I think you are confusing "good" rider with a rider in great condition and who can really ride fast. They are not necessarily the same thing. I have seen reasonably strong riders who could not change a flat. Amazing but true. I have seen people who were old and slow who were adept a nearly all things bicycle and could render aid and comfort to cyclists is distress. I think that knowing how to ride safely on the road, how to deal with mechanical problems, how to diagnose and treat physical problems are all parts of being a "good" cyclist. Riding fast really is not mandatory. Everyone gets old and slows down but that does not mean that they are no longer "good".