While driving back from buying my lunch today, I was thinking about the concept of age, and how much it matters to people. We have a twofold conception of age in this society—we are obsessed both with our chronological age and our mental age. Due to our obsession with numbers in base ten, we see numbers that end with a '0' as being somehow more significant than others, more indicative of a stage of life, than any number in between.
Normally, this isn't a problem. But things get interesting when mental age doesn't equal chronological age. We as society members expect everyone to mature somewhere along an expected scale. We have certain expectations about the emotional maturation of two-year-olds versus forty-year-olds, for example.