Are 19 year olds still teenagers?

Yes, although as others have pointed out are now legally adults.19 does end in 'teen'

The clue is in the word.
Nine Teen

No, they’re obviously middle-aged.

Technically yes but functionally no (because they are now adults and have the rights and responsibilities of an adult).

Yes

They are nineTEEN does that not answer your question?

Yes

According to english humans yes -.-

Yes.

Read the number. Did you have to say "teen?" Then yes.

Yes they are

yes

yes