Sounds like this would be a good personal quirk for your character. While not necessarily 100% accurate, this is a work of fiction which you are creating. As long as you can justify his reasons for going kilted full time, which shouldn't take too much of a stretch of the imagination to pull off then by all means go for it. There are many on this site who do wear kilts full time, although not any farmers that I am aware of.

BTW from rainny Illinois.