Are your fish wild caught? If they are size will not help you. Since clownfish only mature in the absence of a mature pair it is possible you may have a ten year old pair of baby clowns. If they are captive bred I am not sure about exacts, but my pair began to spawn at about age two and a half. If you are serious about this I would get Joyce D. Wilkerson's book CLOWNFISH it takes you through everything you will need to know about rearing and breeding clownfish.