Today, after getting picked up at my bus, a father walked by with an infant. I looked at H and said, "6 months?", she agreed.
Before having one myself... I was useless at aging a child.
I'd ask, "So how old is he? 3 yrs"
"No Andrei, she's 9 months"
"Okay, so she's like 5 right?"
"no, I'm 10"
Now... oh, now... Now I know what physical milestones occur to the month. I know when the head is likely to be up unsupported. I know when certain levels of motor control occur. Now granted, I've learned this not only from having a recently acquired model of my own. But because having one of these devices seems to give you every right to invade in every other parent's life with the obnoxious question, "Ooh, How old"
I think the question is designed solely to give a parent a warm fuzzy about their own child's developmental progress.
Yes... my new super power. Telling the age of a toddler or infant without cutting them in half and counting the rings.