Diego has such a boyish joy to him that fits Matty's pre-slaver innocence perfectly. I remember seeing an interview of his promoting Y Tu Mama Tambien with Gael Garcia Bernal and when he was asked to give a few thoughts on why the movie was being so well received, he was all "I just think we need more love in the world. It's all about love, you know? " which sounds utterly banal, but he made it so sweet and naive in a good way. Yeah, you may have noticed I have a sliiight crush on the guy. Alas, his ethnicity doesn't really fit with Matty's Scottish/highlander background. But yeah, I definitely see why you suggested it manu, we just need someone similar to that.
What about
Rupert Evans for Matty? I know he's not Scottish, but those Brit actors can master all accents from each of the 'home-countries' right? Sure, why not. Anyway, most people have probably seen him in the BBC period drama Fingersmith based on Sarah Waters' book. I don't know how old he is, but from these pictures, which were taken 1-2 years ago, he's pretty boyish looking.
And because I completely love this screen cap:
Hee, he clearly needs to lay off that champagne.