My 21st birthday is in February and I want to go somewhere spectacular for dinner, price doesn't matter... But I'd like to stay on Long Island. I go to school in Suffolk County, but the restaurants don't need to be in Suffolk.
I recommend IL Mulino if you like italian; when you arrive they will begin giving you food right away (cheeses, bruschetta etc...0 and then you will get ready for a fantastic dining experience when you order from the menu.
peter lugers is good bit old fashion for 21 year old
try h2o smithtown, blue in blue point or 21 main in sayville good luck where ever you go and have a very happy birthday also for seafood try cpt bills