What did Noctis do for 10 years?

He encounters the Astral god Bahamut who explains that the Crystal holds the soul of Eos and that Noctis can banish darkness from the world with the power of Providence at the cost of his own life. Noctis sleeps inside the Crystal for ten years, during which time he absorbs the power he needs to fulfill the prophecy.

Is Prompto older than Noctis?

Nova Crystallis on Twitter: "Noctis is 20 years old. Ignis is 22 years old. Gladiolus is 23 years old. Prompto is 20.