I'm trying to figure out Mal's age. Speculation on the firefly wiki puts it at 31.
"Screens from Serenity suggest that Mal was born on September 20, 2468—which would make him 49 at the time of the series Firefly
—though this may be a mistake, since the information screen also misspells his name as "Malcom," and may have been intended to be 2486, making him 31, an age more consistent with his appearance."
Simon was born 2490 so that makes him 27 though he looks a lot younger to me.