I need to indicate my dependent as a full time student but turbotax isn't populating that questions for him. how can i select full time student?

When you enter your Dependents in the Personal Info section, TurboTax asks if your dependent is a full-time student for a dependent over age 19 to determine that they are an eligible dependent. 

 

For a dependent under age 19, there is no need to ask this question.

 

You can still enter Education Expenses for either one of your sons in the Deductions & Credits section.

 

Click this link for more info on Dependents.