I think it's from the era of the Napoleanic wars, Kim. (early 1800's) The chorus gives that indication with the locations mentioned

And it's over the mountains and over the main,
Through Gibralta, tae France and tae Spain,
Get a feather for your bonnet,and a kilt abeen your knee,
Enlist bonnie laddie, an' come awa' wae me.

I'll give my darlin' in Scotland a call tho and get him to post a bit more background for you~he knows a lot about the background of most Scottish folk songs.
~Thyme