At what time does your little one go down for a nap?

My son is 21 months and he goes down for a nap around 11:30-12. I really don't push nap past 12:30 and at the latest he's down is 1 for a nap. My friends daughter is slightly a little bit older than him and she's down for a nap at 1. I'm really not sure how she makes it until 1 because my son is a mess by 11:30 and is almost begging me to go to sleep. He will say about 11:30, "Go night-nights?" He naps for about 2 hours. He's asleep by 8 pm usually and is awake around 6-7 am. Will he gradually be able to stay up until later or is this just his time schedule? Is 11:30-12 okay or is that too early for a 21 month old?