I really struggle on this front and like the original poster, 'can go all night' but an early still puts the fear of god into me!
Agree that you need to calm your mind, I think what is very important is how people aim to get their correct sleep length. For example, if you NEED 6hrs a night to be decent the next morning, don't go to bed at 6hrs -10mins as undoubtably you will toss and turn trying to get to sleep knowing straight away that you will never get the sleep you require. This will therefore make you more agitated and more alert and less likely to fall asleep.
Instead if you NEED 6hrs sleep, make sure you are in bed with the lights off (not watching tv or playing computer) at least 1 hour before your minimum cutoff, ideally more and then you have a decent period where you will not be wound up by the inability to sleep.