R.
It's actually pretty typical for one of the naps to drop at this age one, especially if he's sleeping well at night. What he's doing sounds like a sign to go to one nap. I think what I did was skip the morning nap, eat lunch really early 11:00, then put her down at about 11:30/12:00. She would sleep for about three hours, then I would do bedtime at about 6:30/7:00. That's just an example, go with your son's cues.
As time went on, my daughter would be more awake for longer periods of time in the AM, thus not needing her afternoon nap until 1:00.
Good luck!