13-14 hours a day... down by 7/7:15, up by 6:30/7, and 1.5 - 2 hour nap during the day.
I really think it's a biorhythm thing more than needing a certain number of hours. DD is wiped by 6pm and her mood and temperment are totally different by then. If she happens to go to sleep later than her normal bedtime she does not wake up any later. Similarly, if she has a long nap during the day she's still ready for bed at her usual time. Regularity has been the difference between a really crabby baby and a happy little person.
Have you tried moving his bedtime back by 30-60 minutes? Or starting over and trying to get him down by 7, then experimenting with 1/2 hour increments??
I find that there's an "optimal time" for bedtime too. If we hit it, it's easy. If she gets too overtired it can take much longer. When DD was an infant we were trying to take her to bed with us at 10, thinking infants don't need a regular bedtime. Meanwhile she was begging to go to sleep by 6:30pm! We thought that was too early but we tried it one night and it's been very peaceful since