My boyfriend is always sleeping

I don't get how he is so tired for being only 25.

He wakes up about 430-5am works til 5is sometimes 7. Goes to bed about 9-10 but he only works 4 days a week.

On his days off I'm always up before him and I go bed after him.

He can go bed at 10pm and sleep from 12-2 sometimes later. And go bed by 9-11

And it's the same thing unless you wake him up.

I don't get how he can sleep that much