Different religions have an “age of accountability.”
The legal system has an “age of adulthood.”
And puberty hits us with the “age of awkwardness” (thanks, hormones).

But I propose a new milestone: the Age of Pepto Bismol.
You’re not truly an adult until you have to keep Pepto Bismol nearby at all times, lest the twin demons of heartburn and indigestion take up permanent residence within you.