I have a hard time sorting the age of this particular truck as the company is still in business building very similar vehicles.
From the company history...
Back then, we were known as Wisconsin Duplex Auto Company.
We built Old Betsy, our first four-wheel drive truck, over 90 years ago. And we took on the name Oshkosh Motor Truck Manufacturing Company after moving to Oshkosh, Wisconsin in 1918. Today, Oshkosh Corporation is revered as a leading designer and manufacturer of the world's toughest specialty trucks, truck bodies, and access equipment. No one understands extreme conditions like Oshkosh. Which is why no one builds fire and emergency apparatus, defense vehicles, and commercial and access equipment better.