How do I explain to my 4yo why she has a bedtime but her step brother doesn’t?

Lately, bed time has been a FIGHT. She knows she’s going to bed but her older brother gets to stay awake. She has to be in bed by 9:30-10 but he gets to stay up til atleast 1. I’ve tried saying he’s going to bed too but then she hears him up on his video games and doesn’t want to sleep.