Yes, you can still claim your son as a dependant, since you can still claim medical expenses that you paid for him. In the future, you might also be able to claim college/university tuition transferred from him.
In TurboTax Online, you can enter his income and other info by selecting Deductions>Additional Dependant Information, from the left side menu.
In TurboTax CD/Download EasyStep Mode, you can enter his income and other info by selecting Introduction>Dependants, from the left side menu. In Forms Mode, click on the Dependant icon in the blue icon bar.