There is nothing in the rules to prevent this.
Members in my club wanted the old bird season to be anyage racing, this was put to the fed who again agreed there was nothing to stop them if they so wish but the fed didn't want it. If the club wants to they can make there races anyage and have an old and young bird result, oldbirds only being forwarded to the fed etc to please all members who wish to race any age birds.
I would also sugest that youngbirds are basketed seperatly and not in with old birds, cocks or hens!
Phil