How old is the Japan Egg in Adopt Me?

I'm curious to know, how old exactly is the Japan Egg in the popular game Adopt Me? As a player, I've always been fascinated by the rarity and exclusivity of certain items within the game, and the Japan Egg seems to be one of them. Does anyone know the specific age or duration of time it's been available for players to collect? It would be great to have a clearer understanding of its history and longevity within the game.