How do you make up a 13 y.o. boy to look like an 18 y.o.?  I need to make this smooth cheeked lad look like a 50's greaser stud (don't laugh - we didn't have any boys older than 14 audition for the part).  How do I give him a 5 o'clock shadow and sideburns?

Any help appreciated!

a stipple sponge is quite effective for stubble... just remember to follow the natural pattern of a beard coming in.

emphasize slightly the natural creases in the young mans face.  Frown lines, cheek lines, laugh lines.   You don't have to over do it like you would for old age.  Use a shadow only a couple shades darker than your base.  It may take some experimentation, but not too hard

right about the stipple sponge; an alternative, is just plain soot, smoothed on, then dabbed with a damp natural sponge.  do a test with some physical exercise to see if the kid sweats and the makeup runs. to get the laugh and frown lines in the right place, have the kid scrunch up his face in extremes of frowning and smiling, get the forehead creases, too.  very sharp eyeliner in the deepest part of each crease, all this after base makeup has been applied. the teeniest bit of lighter color beside each line will make them look deeper.  an extremely light film of baby oil under the base makeup will make it a bit more water resistant and easier to remove.  the kid's own hair combed forward in front of his ears, to meet the applied 5-o'clock shadow and kept in place and darkened with styling gel, eyebrow pencil underneath will fill in gaps.  generous amounts of soap and water should remove all of it. clothing a little too tight will make the body look bigger, especially on the upper torso.  a few faked pimples will help, too, on the forehead, cheeks and nose.  practice it ahead of time and take polaroids as you go.