That may be, but while Genos is young, he shouldn't really sound it (and I'm guessing this was a deliberate choice made by the creators, his original voice casting following in this line) since his character('s personality) is hardened and mature beyond his years, given his past (hardships) and his moreover serious disposition, especially initially. An older sounding, unaffected voice is better suited to him. His flat or monotone baritone (ha) and a more controlled/subdued expression, such as his surprise or disbelief, relate his artificial nature.
At least, that's my thinking, and I could be wrong, but "just some dude" >>3042780
(and he doesn't sound anywhere near 30 to me in the English dub, so I don't really know what the fuck they >>3042800
are on about) is a good and accurate description of why it (the Eng.) sounds so bad and off-putting.