'You have a head start, If you are among the very young at heart' - Young at Heart, Frank Sinatra
Because age was mentioned. I don't think that I am good at judging ages of people. Maybe the general decade, but then again some people look older and some younger then their real age (and it is rude to ask, and a lady never tells). As for attitude and mannerisms, girls mature faster than boys so I've heard, some can act childish or immature, while others are wise beyond their years. The young want to be or look older, while older people may want to look / be young again. In other words, I would not be good as an eye witness, if I had to describe any suspect's features : "He looked about um old, and about yay high and this big" *indicates with hand gestures*. How are some people able to judge another person's weight? Or is it mostly in America, as I see it sometimes in American tv shows when something like describing suspects they guess their weight.
Anyway, I think others may think I am younger than my real age, as previous guesses have been lower, which I don't mind. I tend to think of myself as younger (less mature), so that might affect my attitude (though aches and pains like to keep reminding me that I'm getting older). :)