If I'm lucky - 9. If I'm unlucky - midnight 
He's always been a bad sleeper - even when he was a little baby, he never went to sleep after his 7pm-ish feed like his brother and practically every other baby I've encountered but would stay wide awake. Eventually we gave up trying to put him down in his cot as it otherwise meant the entire evening was taken up with trying to get him down, only to then have to get him up for a last dream feed. So he used to sit with us in the evenings in his bouncy chair or high chair quite happily, then have a feed about 11 and go to sleep.
And it's just carried on - his older brother has always been a much better sleeper and is usually asleep before him.
I don't let him stay up - we go upstairs about 7.30-8 ish, get pjs on, have story, do teeth etc and he usually plays quietly in his room, occasionally trotting out to find me or dh for some spurious reason (tonight - 'Mummy I just checking - do my teeth look like a banana?' Yes DS2, your smile is the same shape as a banana. As it was yesterday and the day before that and the one before that...)
Sometimes, particularly at weekends if dh and ds1 are watching a rugby match on tv, he will get to choose a dvd and get pjs on and watch it, often fall asleep to it, but rarely before 9pm.
Other nights when he is just wide awake, I am desperate for him to fall asleep as I want to sleep and don't like leaving him up and the only one awake.
When he is finally ready to go to sleep, he gets into bed and makes a nest for himself out of his bedding and toys, snuggles into the middle of it and falls asleep. I then have to wait a little while until he's heavily asleep so I can shiggle him around and turn his nest back into an ordinary pillow/duvet/tucked in little boy arrangement!
My sis has 3 girls (9,5,4) who are all in bed and asleep on normal days by 7-7.30. because they want to be.
Eldest one now might be a little later, and dsis whilst recognising that 8pm is fine for a 9 yr old, reckons she is missing out on her evenings - she just doesn't realise how lucky she is!