Wearing a grey beard is an easy alternative to ageing the wearer's face with make-up for an "old man" costume. You can make a realistic beard from a small piece of fake fur. Applying "old age" make-up is difficult and it can take 30 minutes for even an expert, but you can make this beard in less time than it would take to apply the make-up and you will be able to use the beard many times.
Measure the wearer's face across the mouth from the front of one ear to the other for the width of the beard. Measure from the bottom of the nose to the desired bottom of the beard for the length of the beard.
Place a piece of faux fur side down on a table with the fur pointing toward you. Faux fur has a nap, the fur points in a single direction. You want the hair on the beard to hang down, so be sure that the nap points toward you when you place it on the table.
Draw a rectangle on the fabric backing with a width and length equal to the width and length of the beard, using a permanent marker. Make the rectangle several inches from the cut edges of the fur so that the fur on the rectangle will be full length, not fur that was cut when the fabric was cut.
Measure the distance from the bottom of the wearer's nose to the top his lips for the width of the moustache. Also measure the height and width of his lips with his mouth closed. For these measurements, consider only the portion of the lips that you would put lipstick on.
Draw a mouth with these measurements on the back of the beard. Center it the moustache width below the top edge of the beard. Draw the top of the mouth with a downward curve from the centre to each side so that it resembles the bottom of a handlebar moustache. These curves should be about 1/2 inch wide.
Curve the top and bottom edges of the beard as desired. An oval shaped beard is most natural, but your character may wear a squarish beard.
Cut out the beard along the lines you drew, cutting only the fabric backing, not the fur. Cut out the mouth also.
Measure around the back of the wearer's head from the front of one ear to the other at beard height. Cut a piece of 1/2-inch elastic this length. Pin the ends of the elastic 1/2 inch below the top of the beard on each side and try the beard on. Adjust the length of the elastic until the beard is comfortable and stays in place.
Sew the elastic on with a zigzag stitch and a 1/2-inch seam allowance. The elastic should be stretched just a bit to hold the beard on.
Part the fur in the middle of the moustache and brush it to each side. Brush the rest of the fur down. Spray the beard with hairspray to hold the fur in place after it's brushed.
Buy fake fur with the longest possible nap. The nap is the fibres that stick out from the fabric backing -- the "hair" of the fur. Use dark elastic if you have dark hair and light elastic if you have light hair.