S.B.
Dear K.,
You are so lucky to have a good sleeper. And so lucky that you have time to adjust his schedule. Just start now.
You're going to have to get him up early and put him to bed early. He won't like it or understand it at first, but you have to do it. My kids always looked forward to summer vacations because they could sleep in, but when I had to work, they still had to go to the babysitter. (They could go back to sleep once they got there if they wanted, my summer babysitter is a teacher and her kids slept in). Be aware that the time changes in and of themselves will make a difference too. Daylight Savings. It was always hard for my kids to go to bed when it was still light outside. On the other hand, when it's dark at 4:30pm in the winter, they are ready for bed by 5:30. My kids were never really day nappers but always slept all night. So....you just have to adjust his little body clock a bit and I think you will be fine. Just start doing it now. Maybe cut out his nap and put him to bed earlier. Try it. Once he's used to going to bed early and getting up early, you can resume the nap thing once he gets used to it.
Best wishes!