We have a set bedtime with a bedtime routine for our 7yo and 3yo, but we're not superstrict about it.
#1 was a clusterfeeder as an infant, who fell into a sleep pattern of nursing off for the night between 8 and 9pm when he was about 6mo old. His bedtime has been about 8pm ever since.
We discovered quickly that while he went quickly to being a kid who could lie down and put himself to sleep easily, he was *not* one to read his own cues as to being tired. He'd push himself to the point of near hysteria if we'd just said, "whenever you're ready."
DD (turning 4 in July) on the other hand, quickly showed us that "down for the night" for her was much earlier. As an infant, she was a bear if we tried to keep her up past 7pm, and even now she goes to sleep by 7:30 usually.
And *I* envy all the "well, we don't have anything to get up for, so there's no reason to go to bed early" people. NOT because they don't have anything to get up for, but because their kids sleep in if kept up late. DS has almost always gotten up between 6am and 7am, though it varies with the seasons (earlier in the summer when its light sooner). We've kept him up until 10 or 11 -- and he's still up with the birds. And cranky as all get out from lack of sleep. So its an earlier bedtime for Bird Boy! DD is pretty much the same-- no extra sleep if she's up later.