Each child is different. Our son has been flying on airplanes since he was a month old, thanks to being stationed with the military in CA and having family in the midwest. We are no longer in CA but we still fly a lot to see family.
Our son asks on a fairly regular basis if we're going to the airport to get on an airplane. He loves to fly.
This being said too, my son has stayed in a lot of hotels as well and is OK with being a homebody but also is happy to go wherever you are willing to take him.
He was just shy of 3 the first time we went to WDW. Surprisingly he still remembers bits and pieces of the trip. It also helps that he has pictures that remind him too. But I am amazed at how much he does remember. We are going in April and he is excited, but that's because he's been before and remembers it. The first time we went, he didn't have a clue and just wasn't excited the way we were. Now, I think he's as excited if not more excited than we are. I'm probably as equally excited as he is because I always get excited when we go to see the Mouse.
You might want to watch the planning DVD a few times as you wait to depart on your trip. He just might get excited. And like several other people said, some kids just don't get it until they are there.
Good luck!