Agree with Smitty that if he wants to play in college he should play with his graduating class. If you don't agree, I'd really like to hear your reasons.
My son played on an elite travel team since he was 14U. Almost always, his 14U team would play up in national level 16U tournaments. By the time they were actually 16U, they won the PG 16U WWBA in East Cobb and they were playing 18U teams the following week. Bottom line is your son should align to his graduating class to get the most eyes on him at the right time. Travel baseball (for end goal of recruiting) is about exposure and separating your talents on the field in your recruiting class. His 16U team can always play up to 18U, and 16U teams are going to have more recruiting eyes on them.
As always, JMO.