|| Unknown, but likely thousands of years old.
King Oberon is the former ruler of Fairy World
along with his wife Queen Titania
at least according the video game The Fairly OddParents: Shadow Showdown
states they're ony figureheads now. Oberon seems to be even more of a figure head than the queen as he seems to only repeat what the Queen says.
As with all video game characters, the canoncity of Oberon and Titania is very questionable, as his only known appearance was within the game.