Linda, I am not sure about the breeding age of most Congo's but Murphy grey's parents were 9 years old before they laid their first clutch.  The breeder had many pairs of greys and they all laid their first clutches the same year.

Maybe I can find an average age for first breeding somewhere on the internet.

I think most bigger birds are much older than little birds when they are mature enough to breed. Bonding can take a long time for the big birds, too, sometimes years.  Some bond quickly though, so you never can be sure how long it will take or even if they will ever bond.

Annie

Here is a pretty good article about breeding greys.  Didn't say how old they will probably be but gives good info about setting them up correctly.

Annie

The breeding age would begin at 4-5 years.  I have read in several sources, that if they are not allowed to choose their mates from a group, the bonding process can be very slow.  Not always, but if the owner chooses the pairing, patience is in order.