Tiredness & Maturity

I was at the neighbor's house a few nights ago and Nina was fighting sleep. Very normal for her age. She was arching her back and crying, very obviously frustrated. Someone made a comment like "why do we have to be adults before we can admit that we're tired?" So true. My baby doesn't want to miss what's going on, she doesn't want to sleep, she is soooo tired but isn't mature enough to recognize it. Will is only a little further down that path. When he's overtired every little thing will set him off. I read several books on sleep habits and the most useful thing I gleaned is this: catch them BEFORE they're overtired. That's easy with Nina - she has the usual sleepy cues of rubbing her eyes or ears or just zoning. Will has NO cues. He goes from being a happy kid who is playing well to a tired little guy who isn't sure what to do with himself very quickly. Unfortunately it is a slippery slope at that point. He can very quickly disintegrate into an overtired fit. Right now it is 2 o'clock, a while past his old nap time (he used to go down at 1 pm.) We realized that scheduling nap times by the clock was part of our problem. Some days he got to play most of the morning and was tired at noon. Other days we went grocery shopping and he might not get tired until 2. My hope is that by this time next year we will be a little more scheduled. He will recognize numbers then. When he's good at that I want to put a digital clock in his room with other clocks nearby indicating when is a good time to get out of bed in the morning and quiet time. I really don't think he'll be taking naps much longer. They're hit & miss right now. He certainly needs the extra sleep!
Anyway, back to my point. It's so common for kids to resist naps and bedtimes. Even sweet, accomodating kids ask to stay up sometimes. Where is that magic moment of maturity? I'm trying to remember.... When did I become old enough to WANT to go to bed? When did I realize that when I stay up I still have to get up in the morning? Was it high school? Was it my first 5-day a week job? Was it when I had to be responsible - when others depended on me? Was it the kids? I can't remember.