Why on Earth was a 60-something cast as a Rogue Romantic Trapper?

In love? I'd say "in heat." Eve wanted someone unlike her father, and Linus Rawlings was about as far from her father as she was likely to find.

You and astockton_uk make a couple of good points about the age thing and what Eve was looking for in a man. Stewart was in his early 50s when the movie was filmed. I agree that a mountain man in his twenties would probably not look as old as he did, but one who had survived into his mid-thirties very well might have looked that old. Living a hard life in a brutal environment can pile on the age lines faster than the years ever could. Just compare how our presidents look when entering office, and then look at how much they have aged in just four or eight years when they leave office. Age aside, Jimmy Stewart with his "well...uh" style was probably the best choice for the role of a trapper. Plus he was box office dynamite.😉

Stewart was fifty-three when the movie was filmed. Baker was thirty.

You gotta understand that the choices for mates were slim pickins' back then. The West was not established yet. She couldn't just swipe right and pick the hottest guy in a 5 mile radius. Also, there was further proof in the film by how the ugly, older wagon lady was behaving as well later on in the story. She didnt even want cash. She just wanted a husband!

stewart realized he was too old for this role.