What's his interests? Does he like food, does he enjoy musicals or enjoy disney films generally?
The restaurant threads might be a good way to get his attention, Disney make some good food, and present them even better for the masses of food porn threads dedicated to each park XD if he's a foodie that might hook him : )
DLP is a hard one to win people over with. I'ld maybe go to Studios first and get Animagique out the way, as it's so weird yet wonderful! (I seem to recall this was actually my first attraction in DLP ever, might be wrong, but we normally go do it first hah)
I'm guessing you'll want to avoid Fantasyland and the more kiddie rides at first. I'ld try the following
Haunted Mansion (it's creepy and certainly NOT kiddie)
Thunder Mesa (it's a rollercoaster but it's one of the mildest - he should be fine on this one, all it has is a few small drops)
Pirates of the Caribbean (again, certainly not kiddie like your b/f might expect)
Buzz Lightyear's Lazer Blast (it's a shooter, with high scores, if he's a gamer he'll be hooked pretty quick)
Optionally try Indiana Jones and Space Mountain, though be warned those are a bit rougher, not as harsh as some UK rollercoasters but do some upside down business.
If you really want to shatter the kiddie ride idea, convince him to ride "Snow White and the Seven Dwarves" or "Pinnochio" and enjoy the results ; ) - if that fails, take him to the dragon under the castle.