I did a directory search and found that John Stille, Jr. (his father John Stille, Sr. was a tailor of some repute) was in business with his brother Benjamin. John was involved in the mercantile business from at least 1793 until 1817, when he becomes listed as a gentleman (living at his dwelling on the SE corner of 8th and Walnut) and his brother Benjamin is the only one listed as a merchant working at the family concern, which is at 33 South Water Street. So, I would say active 1793 to 1817. I will be at Winterthur tomorrow and can perhaps get a more definite date for the 1793 by searching early American newspapers. (The directories are 1785, 1793, 1798, 1800, and then onwards.)
from: Alexandra Kirtley, Curator of American Decorative Arts, Philadelphia Museum of Art, 7-9-2014