S.S.
Anyone ever tell you that average is completely abnormal? :)
That said - keep a journal of when he is sleeping. You'll probably find that he is, in fact, getting his 16 hours or so - just in bigger chunks than most babies his age. As long as his blood sugars at the hospital and his metabolic tests were normal, I wouldn't sweat it any more than I did the baby that only slept - I swear - an hour and 20 minutes, ate for 15 minutes, and slept another hour and 20. :)
S.