Our Disney stuff always ends up in DH's name first, too. Oddly enough, he wasn't even in there when I bought the DVC contract ... yet his name is first on it.
Its not age, since he's younger than me. It might be alphabetical since his last name starts with an "A" and mine starts with an "S".
We're both ethnic, but he has a very complicated difficult to spell last name, and mine is from my caucasian father, so I kept mine (my first name is complicated and difficult enough, I didn't need two). Our son got his last name, if we have a daughter eventually, she will be given mine, and either can choose to change it when they turn 18; both of our last names were too long to hyphenate.
I don't know what Disney's deal is with names, but as long as they don't make it difficult for me to do the reservations, or make any changes without him, I don't care enough to write an e-mail to them about it.
Btw, I'm not sure if this is related but I once reserved a separate DVC room for my brother and nephew whose last name are both the same as mine, so I thought it would be simple and easy. The arrived later than us, so they were checking in while I was in the park, and I got a call that the front desk
couldn't check them in since somehow my 12 year old nephew's name had ended up lead on the reservation.
So I had to come to the front desk to authorize my brother being able to be the lead on the reservation instead of the minor ...
So whatever the program does, it doesn't exclude minors from being leads.