I have nearly 8 and nearly 6 and they have both gone to bed at 7:30 for the last couple of years. DD1 could possibly push out to 8pm but as they share a bedroom this is not really a workable option and DD1 is usually exhausted anyway as she's very energetic during the day. I rarely allow them to go to bed later as they tend to wake too early and get too tired the next day. Bed time routine is to make sure every time that they have gone to the toilet (even if they claim not to need to) and had a very small drink before they get into bed. They know that once they're in bed I don't tolerate mucking around! But this has been their routine since very little so they know that bed time is bed time and if they don't cooperate, their night light gets turned off and they don't like that.
Good luck!