Your ig is big enough to be positively sexed. An experienced vet has to do it. They slide a smooth glass rod down each sac, feeling for the presence of the hemipenes. The sacs that females have are smaller and empty.
They also sometimes evert in view of the owner, and also leave crescent shaped "nocturnal emissions" on the substrate.
Also you can give him an iguana-shaped large stuffed toy that is bright green with a pink tongue and a dorsal crest. The cloth that is the tongue has to be small enough that if he rips it out, he can safely swallow it and pass it. He will do sex play or boss it around if he is a he. Females also like them and carry them around, and both sexes will sleep on them. Sometimes an ig will shred them to pieces, and you have to take it away from them.
Hope that helps.