ok... Science: when kids start being in their tweens and teens, the sleep hormone that is the cause for making people fall asleep (also known as melatonin) starts producing later at night. so kids around 12-16 will fall asleep later at night. on average, kids around 7-11 years old fall asleep at about 8:30 pm. Teens on the other hand will have sleep delayed by about two hours, so a teen that normally falls asleep at 8:30 pm will (on average) fall asleep at about 10:30 pm. So people that tell teens to "just fall asleep" is not exactly possible (I'm not saying it's impossible; I'm saying it's just rather hard) All in all, teens have a harder time falling asleep because the hormone that makes people fall asleep produces later at night, making teens fall asleep later at night.
"After puberty, there is a biological shift in an adolescent’s internal clock of about 2 hours, meaning that a teenager who used to fall asleep at 9:00 PM will now not be able to fall asleep until 11:00 PM. It also means waking 2 hours later in the morning." (A study conducted by nationwide children's hospital)
