You are mixing up two things: In order to be able to transfer BA Avios to Iberia (Combine my Avios), the IB account needs to 90 days old AND active. To make the IB account active, you can transfer Amex points or buy points or credit a flight, whatever.
But even with the IB account being active, it still needs to be 90 days old. How much is the award? If it's cheap, maybe I can help you out, feel free to PM me.