I'm 17 and I get between 3 and 7 usually on weekdays, which my body has adapted to do over time. Probably rather unhealthy. On the weekends I get much more. I'm most productive in the early hours of the morning which is why i've turned out this way.
As long as I was able to get some sleep on the train commute, I was actually able to cope with that tiny amount of sleep pretty well, I think. Looking back at that time, it might very have been the most productive I had yet.
I felt sooo much better getting up at 4:30 in the morning than I feel now when I get up at 6 or 7 (or even later).
I used to feel like I was doing alright on ~6 hours but I often slept 8-10 on weekends. Since then I've started to wake up the same time everyday and there's definitely a difference.
I was always staying up late before school, until 12-1 and waking up at around 7 on weekdays. When I got home I almost always took a nap, from half an hour to a full occasionally. On weekends I stayed up late too, but then I slept a lot longer so I got about 10 hours or more.
Now when me and my girlfriend lives together I've been forced to adjust and I often go to sleep at 10, read a bit before sleep and wake up after about 8 hours even on weekends. I feel a lot better now and I wouldn't want to go back to how I had it only a year ago.
I haven't really thought about sleep deprivation but in retrospect it kinda fits.