Hi LailaK. Sorry it took so long for me to spot this question. I have been asked this same kind of question many times by teenagers or the parents of teenagers. It always seems so strange that teenagers who we think should have lots of energy always seem to be sleeping ... in bed until lunchtime ... on the couch until midnight ... in the car while we are driving them somewhere ... on the beach until they are sunburnt. Parents often think their kids are just being lazy but that's not true. Teenagers need more sleep than they did when they were 9 or 10. There's medical research these days to prove it.
Let me assure you though that teenagers have been sleeping for around 12 hours a day for as long as I can remember. I was a teenager in the 1970s and my mother always said "Good afternoon," when I would get up late on the weekends. It wasn't the afternoon and it used to annoy me. When I had my own teenagers and their grandmother was visiting she would say "Good afternoon" when they stumbled from their bedrooms, as though she disapproved that they had slept in. I don't mind my kids sleeping. I think it is good for them.
One of my now adult daughters used to fall asleep on the couch while watching television. I knew there was no way her dad would let her keep sleeping there after he woke early in the morning so I would lead her downstairs to her bedroom at about midnight and cover her in bed so she could sleep as long as possible before having to get up and get ready for school.
That same daughter now lives in her own home and leads her own life and never has any trouble staying up late and getting to work early the next morning. She's in her 20s now and past the sleeping beauty teenage years.