Fine Antique Mirrors has dated this piece to the 1800s.

Original wafer thin convex mirror plate, which has a shallow convex curve and overall foxing. Plate re silvered most probably in the late 19th century.
Original backing board, complete with T. Fentham makers label.
79 cm diameter or 31 1/8" diameter.
Thomas Fentham
Trading at 49 Strand (1777); no. 52, ‘opposite Old Round Court’ (1778–93); no. 51 (1784); and 136 Strand, near Somerset House (1794–1820).
Fine Antique Mirrors has dated this piece to the 1800s.
Specializing in antique 18th/19th century gilt mirrors. Gilding restoration undertaken.
You can view the stock and full dealer information on the Fine Antique Mirrors Profile Page