A Metropolitan recipe appears in the 1935 The Old Waldorf-Astoria Bar Book, but it calls for 2/3 Manhattan bitters (obsolete, possibly similar to Amer Picon) and 1/3 vermouth. While that sounds like an interesting mix, the more common brandy recipe has been noted with the year 1900.
There are other cocktails that have taken the name "Metropolitan." Possibly the most popular is one made of Absolut Kurant Vodka, cranberry and lime juices, and (sometimes) triple sec. It is very similar to a Cosmopolitan and was created during the 1990's in New York City.