Dylan is old enough to vote. He is also old enough to serve in the military, which means he is old enough to kill people for his country. But he is not yet old enough to drink. He is not 21.
In Spanish class when the professor asked him conversationally (for practice) if he drank, Dylan became confused and didn’t know what to say because of course he drinks (he’s in college) but he didn’t want to admit to anything illegal so he tripped over his tongue and pretended he didn’t know how to say it in Spanish.