I can’t get my sister’s comment out of my head. The one I told you about, that she wished she had noticed the day before her daughters grew taller than her.

Maybe it was the setting in which she said these words — a 19th birthday celebration, the birthday girl-woman’s feet balanced on the tectonic plates of childhood and adulthood, bumping against each other.

Or maybe it was the wide blue ocean behind my sister as she spoke matter of factly about this milestone going unnoticed, that taunted, rolled its eyes and shrugged at this infinitesimal, irrelevant tendency of children to grow up, that impressed her words on me.

Or maybe it’s because, as my friend Monica told me, once they start high school everything speeds up. It’s the last measurable stop before adulthood.

They are rare, these concrete ways of measuring maturity. I know one more:

Almost, but not quite.