I am 51, my good friend is about 63, his two sons are 41 and 39. The sons call me "Mr." and "sir" without fail. It makes me feel even older than I usually do. I cannot get them to stop. I don't know if it is relevant that they are African Americans in the US South. But it is extremely respectful and polite especially since I have done nothing to deserve that extra degree of respect other than being polite to them.