Can I still carry my son, he's 20 years old, a college student, and he also works?

Yes, you can claim your son as a dependent provided he meets the rules below.

• Your son must be a U.S. citizen, a U.S. national, U.S. resident, or a resident of Canada or Mexico.  There are certain exceptions for adopted children.
• You can't claim someone who is claimed as a dependent on another tax return. 
• You can't claim someone who's married and files a joint tax return. 
• They are 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's no age limit if your child is permanently and totally disabled.
• The child must live with you for more than half the year. Living at school as a full time student does qualify.
• They may have a job, but they cannot provide more than half of their own support.

See the TurboTax article Rules for Claiming Dependents on Taxes