Son turned 20 but still in 3rd year of college. He earned some income from internships and jobs. Can we claim him as dependent and should he file his taxes as well in TT?

You may be able to claim your son as a Qualifying Child dependent if:

• The child must be related to you. The child can be your son, daughter, stepchild, eligible foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, adopted child or an offspring of any of them.
• Your child must be under age 19 or, if a full-time student, under age 24. There is no age limit if your child is permanently and totally disabled.
• Your child must live with you for more than half the year, but several exceptions apply (ie. away at school).
• The child cannot provide more than half of his/her support.
• You must be the only person claiming the child
• The child must be a US citizen, resident alien, national, or resident of Mexico or Canada.
• The child cannot file a joint return with his or her spouse. 

Your claiming him as your dependent will not disqualify him from filing his own return.

If your dependent earned more than $6,350 in W-2 wages or more than $400 in self-employment/1099/MISC income, he/she is required to file a rerun. For less W-2 income earned, the dependent may elect to file a return to obtain a refund of his/her withholding(s)

If the dependent files his own return with TurboTax, he should check the box Someone else can claim me on their tax return in the personal information section.