A Long Time Ago

From Halopedia, the Halo wiki

A Long Time Ago is an achievement in Halo: The Master Chief Collection. It is unlocked by playing Halo 4 on the 6th of any month - the day in November, 2012 when the original game was released. The achievement will unlock as soon as the player begins a campaign mission or multiplayer match. The achievement is worth 5 Gamerscore.