DS6 went through a period of this. When he'd start demanding things, I'd ask him to repeat it as a 5yo would. If he refused or started revving up, I'd start subtracting 1's from his age. "Now you are 4, bedtime is 7:30" "Now you are 3, bedtime is 7:00". It took about 3 times of early bedtimes and he determined that he preferred being 5.

Shari
Mom to DS 10, DS 11, DS 13
Ability doesn't make us, Choices do!