From Shawn:
After 40 you are old. I believe Dostoyevsky put in best in Notes from Underground:
"I am forty years old now, and you know forty years is a whole lifetime; you know it is extreme old age. To live longer than forty years is bad manners, is vulgar, immoral. Who does live beyond forty? Answer that, sincerely and honestly I will tell you who do: fools and worthless fellows. I tell all old men that to their face, all these venerable old men, all these silver-haired and reverend seniors! I tell the whole world that to its face! I have a right to say so, for I shall go on living to sixty myself. To seventy! To eighty! ... Stay, let me take breath..."