“Why does it take so long to wake up from anesthesia?”

Teenagers love to sleep anyway. Surgery can be very stressful on anyone. Teenagers tend to overthink things, read about anesthesia, hear stories about others with anesthesia, and worry. You all act calm, but on the inside are worried about, will I wake up or not in the middle or the end, will things go okay, etc. So, when you are out of anesthesia, you get what I call the "let down response," which is that you are glad that all went well, you are relieved and just sleep because you most likely did not get good sleep up to a week before the procedure, and had been stressed about the procedure and anesthesia. Depending on the case, you will get some narcotic/painkillers that will relax you as well.
Hope this helps.

That is not correct. If a person has delayed awakening, it's a problem. Maybe metabolic, and it has to be evaluated.