"In 2006, Joss Naylor ran 50 miles up and down seventy Lake District fells, ascending more than 25,000 feet in 21 hours. Not his best performance, but to be fair, he was 70 at the time."That post gives more context about fell running and a video. So, you have someone who's already had children if they wanted to, they've had a long life in the area and know it as well as anyone can, they can run for days, ghosting invading forces. Hell, with the abilities these fell runners have, they could keep tabs on an enemy's position by running back and forth between it and wherever they're reporting.
Okay, maybe add in proficiency with a bow, but I see them mostly as scouts. Not an interesting archetype to play I suppose, especially in a group where you wouldn't be able to utilize your running ability without leaving them in the dust, but this will probably be the standard for wilderness roaming rangers in my world.