Green iguanas start to reach sexual maturity in 2 1/2 to 3 years, when males start to go through their breeding cycle they tend to stop eating so they can spend more of their time displaying what a impressive male they are and patrolling their territory. This is what you've been starting to see, so if he doesn't eat a whole lot i wouldn't worry, just make sure you keep food out everyday he'll go back to eating normally.