The Sky Crawlers: I Cavalieri del Cielo (2008)

Blurb:
From Mamoru Oshii, the world-acclaimed director of “Ghost in the Shell” comes an award-winning story of an exciting but endless war with heroes too young to understand the meaning of their battles. A group of eternally young fighter pilots known as Kildren experience the sudden loss of innocence as they battle the enemy in astonishing dogfights above the clouds. With his only childhood memory consisting of intense flight training, the fearless teenage pilot Yuichi’s dogfights coexist with his struggle to find his missing past. When his beautiful, young female commander Suito is reluctant to discuss the fate of the pilot that Yuichi is replacing – or the strangely perfect condition of that pilot’s former aircraft – Yuichi’s curiosity becomes heightened.

Source: www.anisearch.com/anime/4363