I've started or added to numerous threads over the last few years on this subject (I'm guessing about 5 previous threads) but I think I know the answer now. Its not necessarily when you decide there is nothing new that you want. Its not when conversations with friends and family primarily involve your medical ailments. And its not when you go out in public wearing shorts and high black socks (but this is close). The real answer is that you are old when or if you suddenly drop dead without warning, while many might be saddened, few will be shocked. When you are old enough that instead of total surprise, other folks next comment is "Well, he WAS xx after all". At 81 I know I am old, and approaching "really old" (when I worked in the nursing home field, we considered 85 as the beginning of really old age). I feel quite sure that if I don't make it to tomorrow, some would just shake their heads and say "Well, you know he was already 81!".
One advantage, however, of getting old is having a decreased concern for what other people think. I know much of my family, and many old friends are lifelong liberals and still think the Democrat Party is the one that cares, and are appalled that I am a Trump supporter. Many of my family think that my membership in the NRA shows signs of insanity, and the fact that I still ride motorcycles just convinces them that I am beyond hope. And I would find it hard to care even less than I do that they think that and feel the way that they do.
One advantage, however, of getting old is having a decreased concern for what other people think. I know much of my family, and many old friends are lifelong liberals and still think the Democrat Party is the one that cares, and are appalled that I am a Trump supporter. Many of my family think that my membership in the NRA shows signs of insanity, and the fact that I still ride motorcycles just convinces them that I am beyond hope. And I would find it hard to care even less than I do that they think that and feel the way that they do.