I know several people like this, my gut tells me it's not super uncommon.
It was not always like this , but the older I get the less sleep I seem to need. In my 20s would feel groggy on 5 hours of sleep, but in my 30s ( current age ) I feel groggy if I get more than 5 hours sleep.
I haven't been able to "sleep in" since I was probably 15 or 16.
Some people probably call this being a morning person, to over simplify it heavily.
Edit: if you do some light googling there is a substantial anoint of data on the internet that claims 8 hours of sleep is too much and 6 is closer to ideal for full grown adults. So getting 4-5 and a healthy dose of exercise does not seem in the realm of supernatural to me. Give it a shot! ( don't leave out the exercise either )