How old is Karl?

I had a thought tonight. When Alex talks to Karl he says "Your father will kill me." To which she replies "Is he really my father." Now she says it in a manner which suggests that Karl would know. We've assumed that Karl is about Alex's age. 17 or so. But what if he's older? What if, like Richard, he's an unaging Hostile? This would at least partly explain why Ben seems so violently opposed to their romance. If Karl is really quite a bit older than Alex, perhaps older than Ben, then what father wouldn't object. It would also explain why it was Karl who delivered Ben's X-rays to Juliet. Maybe he's just a gofer but if he's older than he looks he could have a significant job.