Hi, L - our best thread on this song is this one (click). We put an "origins" tag on the threads that give the best information about the beginnings of a song. I didn't see anything in the thread prior to about 1840, but there are several from about that time that may actually be older. there are theories that put the song back as far as 1688, but I haven't seen a text and tune that date back to the 18th century. Good luck.
-Joe Offer-