I'm not a New Yorker (just a wannabee) but we often visit the city so as a tourist I'd say your son should definitely go into Manhattan. While the tourist sites are well-worth seeing, with such short time available he might be interested in taking the circle boat tour which is about 3 hours, will take him all around the island, and give him some great information about the city, its history and culture. http://www.circleline42.com/

In the evening, I'd suggest Greenwich Village - he's young, he'll definitely get into the groove with all the restaurants and bars with live entertainment - or the area around Washington Square (New York University) where he'll meet people his own age. The morning before he leaves, he could go to Central Park and the area south of it onto Broadway, Times Square, etc. and walk around to get more of the flavour of the city.

Alternatively, he could visit some of the fabulous museums if that's what he likes to do. There are too many to list.

New York Ziners may have suggestions on places to stay. I found this site, which may be helpful. http://www.spanishnewyork.com/hotels-in-manhattan.html

Lucy, Toronto