Is it il pris or il prit? in french?

"Il prit" is the passé simple (a literary tense). It's like you're reading a novel and it's written "He took ages"

"Il pris" doesn't exist. "Pris" is the past participle of the verb "prendre".

You can't use the past participle as a verb without an auxiliary (an helping verb).

So "He took ages" in a non literary way is "Il a pris une éternité"

And finally, "it" can be "il" (he), "elle" (she) or "ça" (this/that).

But, here the "it" of "It took ages" is impersonal so it's "Ça a pris une éternité"

If "it" is not impersonal, then the sentence must specify what took ages and the verb "mettre" is better suited instead of "prendre"

(Le robot) Il a mis une éternité à s'éteindre = (The robot) It took ages to shut down

(La fleur) Elle a mis une éternité à faner = (The flower) It took ages to wilt

You need context to know what to write.

il pris