The original graphic novel will be the first from Top Cow Productions' creator-owned imprint Minotaur Press.
Gage will team with The Darkness artist Jorge Lucas on the tale of a retired mob enforcer.
"I think the initial inspiration came from reading more and more stories of people in what we would call their 'sunset years' - seventies, eighties and above - accomplishing physical feats most of us would consider impossible for people their age: running marathons, fighting off muggers - hell, look at Clint Eastwood. He's 80, and would you mess with him? I wouldn't," Gage told Comic Book Resources.
"From there, I started thinking about what it would be like for someone from an era gone by to suddenly be revisited by a violent past in a world that's passed him by... and what would happen if he was still well equipped to face it.
"Sunset combines elements of noir, revenge stories, crime capers, romance - but at heart it's what Duane Swierczynski calls 'Old Man Noir.' It has common ground with movies like Unforgiven, Taken and The Limey."
Gage currently writes Avengers Academy and Angel and Faith.
Sunset will arrive in shops on July 18.