As a rule, teenagers require 8-10 hours of sleep per night. If you feel rested after 7, then you are fine. If not, try cutting back on any caffeine, exercise during the day and set a bedtime routine without stimuli such as bright lights, TV, noise etc.
7 hours really?! Wait until adulthood, you be wishing one was 13 again. Seven to nine hours of sleep is the norm for most people, any more than that is due to physical/mental health issues. (Illness, stress or depression).
I had the same problem, it's usually because u r not organizing ur time... 7 hours isn't really good, if u want to be more healthy and energetic then sleep 10 hours :) and when u go to bed, try to think of good stuff and not bad things that happened to u earlier in the day ;)
Teens need more sleep then the rest of us. Try to avoid caffeine found in more than just coffee. Do not shower before bed even if it feels good. Do not read or watch TV in bed. Your bed is for sleeping only. Try some white noise such as a fan. Keep your room temp cool. Avoid naps even if you are really tired during the day. Go to bed an hour earlier. Your body keeps score of missing sleep. Sometimes you can catch up your sleep on weekends. If you still owe a sleep debt it will affect your thinking. Good luck. Oh and here is a warning: it only gets worse as we age. 7 hours of sleep would be a welcome miracle for me. I have no trouble falling asleep but I can never stay asleep. Unfortunately I must take sleeping aides prescribed by my doctor, occasionally, when the lack of sleep starts fogging my mind.