Jennifer Lopez turned 43 in style last night by partying on a giant boat with her much younger boytoy.

The hot mama looked amazing in a tight, backless red dress as she danced the night away on a yacht in NYC. And by J.Lo's side all night is 25-year-old boyfriend Casper Smart.

The two looked very lovey-dovey while dancing together on the boat. And from the looks of the photos, Casper may have given Jennifer a new necklace as a present -- as she was seen holding onto the new accessory with a romantic look in her eye as they talked.

more pictures at my site...