That is really a difficult question to answer. Even if you do have a male and female, it isn't a guarantee that they will pair off and start breeding. Cichlids especially choose males carefully, they may not choose to breed with any old male that is stuck in the tank with them. To hazard a guess, you could probably look for signs of probable breeding by 14 or 15 months. I myself haven't experienced Oscars much younger starting to lay eggs.
You may experience your fish going through all the signs of wanting to breed, lip locking, cleaning the slate, excavating substrate, however they may never lay eggs. I have a female Oscar that has laid on several occasions, even though the fish that spends most of its time with her helps look after the eggs, as of yet, they have not hatched. You are just not going to know until they successfully breed.
