My son is 11 and has been sleeping later then normal. could he be going through a growing spurt?

Very possible: It is very possible that a growth spurt may be occurring. Some boys at that age may be going throug puberty too.

Yes: The average 11 yo would be expected to need 9-10hrs/d with more added for such activities as sports practice or studying for exams. If they create a sleep deficit on some days they would usually catch up on others. Naps during family activities, studying, in class or similar events would be a sign of a sleep deficit. Growth spurts can add to need.