Sometimes people get certified first (my recommendation) or get certified while on vacation (looks like your nephew's preference).My 18 year old nephew would like to get certified for scuba, and is thinking about taking his first dive trip over Christmas break. He tried it once at a resort and loved his one and only test dive. Can anyone recommend a good choice for a beginner's first dive vacation? I think Hawaii would be pretty chilly and possibly choppy that time of year, but what about Roatan, or the Florida Keys, or? I'm a diver and am excited to take him somewhere, but don't want to make his first trip a bad experience - so I'd appreciate any suggestions!
Would your nephew consider south Florida? Say Ft. Lauderdale? Many of us would highly recommend 5-Star SCUBA Dive & Snorkeling - Get Certified, Sidemount, and Technical Diving - run by Ryan Custureri and @LandonL.
He could continue afterwards towards the Florida Keys.
I would recommend finding a place with quality instruction (neutrally buoyant and trimmed during the ENTIRE course, finning, situational awareness, etc.). It is hard to top Ryan's results with open water students.
I guess it comes down to does your nephew want to just go diving or be a diver?