My son is only five, but I'll bite.
1. No
2. My thought is this: I am the adult. Kids do not know what is 'best' for them... if they did, they would hatch from eggs and walk away from us. :)
Reasons: I know how much sleep my child needs. He, on the other hand, does not. His 'bedtime' is seven-thirty. If he's tired, he'll sleep then. If not, he can stay up until 8 on school nights, 8:30 on other nights, looking at books quietly in his room.
I do not believe my son has enough information and self-regulation-- and will likely not have it until he is much, much older-- to make choices regarding health and nutrition for himself. I don't let him do the grocery shopping, he doesn't get to choose his meals, he doesn't get to choose if he gets shots... Children need adults who take charge and set the ground rules.
I have two neighborhood families I like very much. That said, they choose to let their children 'decide' about some of these things, and sometimes, their kids are a mess the next day because they haven't slept well. Then the parents complain that they can't do this or that because the kid is cranky or needs a nap... and then the child with the nap stays up late again and the cycle continues.
No thanks.
At six, his bedtime will likely be 7:45-8:00, because he'll be going to full-day kindergarten (he's half-day now) and we still want to leave room at the end for him to wind down looking at books. So, pushing things 15-3- minutes later at that point seems reasonable.