Ecuador will, however, get a three-point deduction at the start of the next round of World Cup qualifiers and will pay a fine of 100,000 Swiss Francs ($101,605.36) for the "use of a document containing false information", CAS said.
Ecuador were drawn in Group A alongside Qatar, Senegal and the Netherlands and the South American team were set to play the hosts when the World Cup kicks off on November 20th.
In September, FIFA had dismissed Chile's appeal following their original complaint that Castillo was born in Tumaco, Colombia in 1995 and not in the Ecuadorean city of General Villamil Playas in 1998, as stated on his official documents.
Castillo played in eight of Ecuador's qualifying games - including twice against Chile - for the Qatar World Cup as they took fourth place. Ecuador have denied that the player was ineligible.
Peru finished fifth in South American qualifying, missing out on the last automatic spot for Qatar while Chile finished seventh.
