You'll find that most teens today are allowed to have unfettered access to texting while in bed, they'll end up staying up all night long and sleep well past noon the next day if allowed. It's a matter of responsibility and discipline. We still pay for DS phone and I checked his activity last year when I heard a complaint of being tired all the time....I found that the "LOL's" were coming in till the wee hours of the morning!!!
We fixed that problem quick: shut your damn phone off!!! At the very least at midnight if you expect to sleep!
He was pissed that I looked at his phone records but, it did two things 1) he now wants his own phone account
and 2) he realized that he was staying up way too long at night and playing silly games with people that didn't have the same responsibilities he had the next day.
I also never let him sleep past what thought was decent hour in the morning over the last few years. I know...mean dad but, I laugh my butt off when my son complains that: "all his friends sleep past noon everyday when not in school". Good for them I say, they'll be sleepy and unproductive all day, break the cycle!
I know that's harsh, but it's the reality today with phones/cameras on them.
7 hours of sleep is more than enough.