Miss Chicken wrote:
a) a person's age
I've gotten so much better over the years, as I myself get older.
When I was in my 20s, I was at least a decade off when it came to guessing someone's age. I would think, "This lady must be in her mid-40s" only to find out later that she was well into her 50s. Now I'm actually pretty right on within a certain age range. There will always be exceptions, of course, based on a person's ethnicity, health, lifestyle, and aesthetic factors.
I have a somewhat accurate technique that I always use: When in doubt, I look at the person's elbows (that's right) and see how wrinkled they are.
b) a person's height
c) a person's weight?
As a guy, it's harder for me to guess a woman's weight than a man's weight because of differences in body and muscle composition. I would probably be able to guess someone's weight in terms of the range, as in 170s, 180s (lbs). As far as height, all I do is compare someone to my own height and figure out the difference.