I compare people to me and usually mess things up.
I'm 49 but I'm told I look 40. When I look in the mirror, knowing I'm 49, and then look at people who are my age, they look old to me; people who are younger look like kids to me.
I'm only 5' 1" and am used to having to tilt my head up to look at most adults. I judge height only by quickly measuring myself against them. Visually, that is.
I'm...let's say "chunky"...and my actual weight is more than it appears. By easily 20 or more pounds. So someone who is my weight is physically much bigger than me. Not sure how that happened. Even my doctor doesn't understand that one, but says I carry my weight well. But still need to lose some.
Hubby, conversely, was always good at guessing age, weight, height, and even income where we used to work (in the 1980s). Amazingly/annoyingly observant.