You can stitch this on any count you like.
Keep in mind, though, that if you use 14 ct, the size of the finished design will be larger at 28.5 inches x 21.4 inches. Add 6 inches to each measurement for framing/finishing and you will need a piece of 14 ct Aida that measures a minimum of 34.5 inches x 27.4 inches.
Mary