I think it depends so much on the child- as with all things. My 5 1/2 yr old is uber responsible and doesn't do anything he's unsure of w/o asking. He usually sleeps until around 7, but every now and then he's up early. Around 4 1/2, we gave him a clock in his room. He is allowed to play quietly in his room until 7am if he is up early. (We put this rule into play because sometimes he would wake up at 4am for no reason and figure it was time to get up and play. We explained to him that he needs his sleep and should really try to go back to sleep at those times. So, in the beginning the rule was that he wasn't allowed to get out of his bed until 7 - which was his normal wake up time - but could read quietly in it if he wanted to. This encouraged him to go back to sleep on those really early wake ups. Once he got into that habit, and was better able to read the clock, we changed it so that as long as it was after 6 he could play in his room. The no Living Room until 7 rule is because he's not very good at being quiet and would often accidentally wake his little brother up if he was playing there.) Once it is 7, he can come get us, or go out and watch tv or play w/ his toys in the living room. (We have a ranch, so the living room is just down the hall from our room.)
I used to set up a little snack for him in "his drawer" in the kitchen so he could sit on the couch and watch a cartoon w/ a little dry cereal or dried berries. (We would set the tv to the Disney Channel or Noggin the night before. He was only allowed to turn on the tv using the button on the set, not touch the remote - this way we knew he wouldn't accidentally flip to something that could be upsetting.)
Usually, I'm up once the tv goes on, but it buys me a few minutes to wake up peacefully instead of being shaken awake... which makes for a much happier Mommy! (I'm NOT a morning person.)
I don't really stay in bed too long after he is up, but I know my husband does some days when I work early.
We have a 2 yr old as well, and once he's up, we're all up. I'd never put the 5yr old in charge of the 2yr old w/o being fully awake and nearby. And, honestly, if things had been reversed, I'm don't think I'd have been able to let my second son up by himself at 4 1/2 (can't really say since he's not that old yet, but his personality is much more... um... adventurous!)
Long story short - My 4 1/2 yr old was ready to be up on his own for a short while with limitations. And with me w/in earshot down the hall. Another child (my second for examplt) may not be. Now that he is 5 1/2 he really is capable of funtioning on his own in the morning. And I do indulge in sleeping an extra 20 minutes or so sometimes. But, mostly, I miss him all week and look forward to my quiet mornings. So, I haven't tested the theory too much yet. (Not commenting on you not wanting to get up - I have those days too!)