First off, take an examination of how closely you alraedy look 50 plus.  You may not need much make-up.  I am being honest not flippant.  Next, determine how far away from the audience you will be and how bright the lighting.  If you are a distance away, I would suggest adding lines to the already natrual and existing lines on your face - in particular the smiles line from your nose to the edges of your mouth, under the eye and the crows feet at the outer edges of your eye.  Also, apply a line above your eyebrow.  You can determine these lines by smiling, squinting and raising your eyebrows.  Do not use black but use a brown or dark purple liner - very sharp!!  To create more depth, you can highlight the lines ON TOP with white.  The skin oft gets ruddy with age and you can use a stipling brush or the end of a stiff brish to ad ruddiness and texture.  One more idea; darken with a powder blush underneath your jowels.  Play around.  Good luck.