When people say, "You don't look your age" – or “I’d never have guessed you were that old,” we are supposed to think of it as a complement.
But to me, the developmental psychologist, it means that they have a preconceived idea of what "my age" should look like: a preconceived notion or bias about certain ages; especially “older” ages. We are our ages; therefore we do look our age!
We grow up with many biases about people and other things because having biases is a part of being human. Your biases are based on your family, community and culture. [I write more about biases in You Can Totally Screw Up As A Mom And Still Raise Great Kids.]
Certain biases are neither good nor bad, but it is important to know your own biases as they affect what you see, do and say.
And many of our biases center around "ages and stages."
We often compartmentalize people as being and looking certain ages and stages – and then we often comment on how they are not doing as we expected!
"Stop acting like a child!"
“Act your age!”
“You are too old to be acting like that!”
“You are too young to be acting like that!”
The next time you are tempted to say anything relating to a person's "age," stop and think about what you really mean!
Comments? Thank you 
I am 18 and people think I’m 14
People ask me if my 13 yr old sis and i are twins and I’m like NO
Then when i say what age i am they either a) don’t believe me or b) ask me a math Q
I such @ math so i never get it right. thats not fair, if it was an english Q i’d ace it
we are an ageist world!0( Its sad and very uncomfortable… I love to have bare feet, puddle stomp…go out in the rain just because…. I have been told I am not childish..just childlike ;0 and that to me was a wonderful complement….Never lose the child inside no matter how old you are…Its where all the magic lives .0)
My thoughts precisely. Thank you Tess [I say as I sit here barefoot :-)]
Lynn