I admit that Mateus's face suggests that he's closer to 30 than 40 but his voice in both versions sounds middle aged. (Mind you going by voices doesn't help much since in Japanese Squall sounds in his 20s, Bartz sounds like a teenager, Laguna sounds middle aged, CoD sounds like an old crone, Zidane's pitch flails all over the place and Kuja flips between teenager and 20 something depending on the mood. However all of these save Laguna are probably intentional.) However his appearance to me suggests older than 30, though this is probably due to the fact that he has a thin face. That and his hands are rather aged from an artist's standpoint. (I've studied them. THEY HAVE NOTABLE LINES.)
I think Mateus's attitude also helps me think that he's around the same age as Kefka because Mateus certainly does not act at all like a young person and every aspect of his behavior gives off the aura of experience. I can believe that he's younger than Kefka physically but the way he acts certainly makes me think that he's in his 30s. Also the way that Kefka acts around Mateus and Ultimecia comes across to me as though he views them as the closest thing to contemporaries which makes me a little more inclined to believe their ages are similar. (I wouldn't be surprised if Ulti is the oldest of the lot.)
And again I am amused that the old hats were, in the Japanese version, indeed voiced by old hats. (The ages ranged from 69-39 on the Team Chaos seiyuu side when Dissidia first came out. With Team Cosmos it was 44-24.) A good chunk of the cast were voicing someone either half their age or 15-20 years younger. (Midorikawa probably wins since he was 38 when he first did 18 year old Firion. Second place goes to 35 year old Romi Paku voicing 16 year old Zidane. If we knew Mateus's age then we might be able to factor the then 49 year old Kenyuu Horiuchi in there.)
WHY DO I NOW HAVE THE IMAGE OF GARLAND AND THE FOUR FIENDS SKIPPING DOWN A YELLOW BRICK ROAD?
I think Mateus's attitude also helps me think that he's around the same age as Kefka because Mateus certainly does not act at all like a young person and every aspect of his behavior gives off the aura of experience. I can believe that he's younger than Kefka physically but the way he acts certainly makes me think that he's in his 30s. Also the way that Kefka acts around Mateus and Ultimecia comes across to me as though he views them as the closest thing to contemporaries which makes me a little more inclined to believe their ages are similar. (I wouldn't be surprised if Ulti is the oldest of the lot.)
And again I am amused that the old hats were, in the Japanese version, indeed voiced by old hats. (The ages ranged from 69-39 on the Team Chaos seiyuu side when Dissidia first came out. With Team Cosmos it was 44-24.) A good chunk of the cast were voicing someone either half their age or 15-20 years younger. (Midorikawa probably wins since he was 38 when he first did 18 year old Firion. Second place goes to 35 year old Romi Paku voicing 16 year old Zidane. If we knew Mateus's age then we might be able to factor the then 49 year old Kenyuu Horiuchi in there.)