It’s been 3000 years is a famous quote from the Pokémon games Pokémon X and Y from the character AZ.
Online, it is used as a reaction image to express feelings of catharsis at the arrival of an awaited event.
The sixth generation of Pokémon games, Pokémon X and Pokémon Y was released in 2013.
The games feature a character, AZ, who is a travelling Pokémon trainer and who encounters a unique Floette Pokémon, the Eternal Flower.
When AZ sees the Floette, he collapses to his knees and exclaims “It’s been 3000 years”.
“It’s been 3000 years” showed up on the r/pokemon subreddit in December, 2013.
The reaction image would then be used on Reddit, as well as Tumblr.