Broadly speaking, it lasts from ages 10 to 20, with a greater salience between, say, 12 and 15 years old.
This is the period of life (at least in my life) when the Big Questions got the most attention. These questions concern such matters as: What is the meaning of life (if any)? Is there a god? What sort of a god? Do we somehow outlive our corporeal existence? Why is there so much suffering? Why does anything exist? And do humans have free will or are we mere automatons shoved around by a radically deterministic universe? I well remember anguishing over these kinds of questions.
In my junior year as a Berkeley undergrad, for instance, I remember the free will and determinism question being associated with a long patch of depression — whether as the depression’s partial cause or partial effect I cannot say.