J.H.
What helped me get my 2.5 yo to sleep longer was to have a routine. She eats lunch between 11 and 12, then I put her down for her nap after lunch. She has a full belly and tends to sleep for 2 hrs sometimes more. At night we get her into her PJ's and put her down after reading a couple stories between 7:30 and 8pm. She will sleep until 5:30-6am. Sometimes she sleeps later but its rarely. I think if you started doing things the same way everyday you will find that he will get the sleep he needs.