Made by my Uncle using an old car axle spring. He was a carpenter by trade and made all his own toys as a young boy back in the mid 1900s. He died at 96 and was older than my Grandmother who was born in 1907. His favorite toys were covered wagons and wheeled hay baling wagons that actually bailed dried grass and had a thread mechanism that you could tie the bale. It was a rough ride at 5 but I loved it, you couldn't break it.
I would have envied you your horse. At five my first horses were stick stick horses. The best one was an old broom worn down to a nub sweeping dirt floors but I tied a rope bridal on that broc and he was a good one. Later on my uncle gave me a couple of work horses better known as saw-horses. They were useful but not nearly as much fun.