Youth is not required, but the wild, reckless abandon, the perceived invulnerability, the strength to weight ratio, and the adventurous nature of youth is mandatory.
Choose a good day. An early summer day while skipping a friday from the end of the school year is best, but any day with friends nearby will work. Friends are mandatory. They will run helter-skelter down the hill with you. They will share the adventure. They will laugh with you at the breakneck world rolling by. Leaves should be full, on this chosen good day, and flowers should be in bloom. Bumblebees the size of your thumb should be in flight. Snakes should be slithering through dry grass.
Choose a good hill. It must be steep enough to be difficult to walk down. It should be grassy at least, but completely untended grass is best. Littered with soda cans and overturned shopping carts, broken glass and sandstone rocks jutting out of the ground.
Stand at the top of the hill, brimming with energy and good feelings and laughter. Build your karma. Think happy thoughts. Run along the top of the hill a bit to warm up those legs, and then plunge down the slope, full speed, hard core, no fear. You are alive. A body in motion tends to stay in motion. You are a machine, all elbows and sinew and inner ear. You could not stop if you had to, and trying would be suicide. Your stride stretches as you build up speed. You make twelve foot leeps over old truck tires. Your shoes swallow their tongues, which bunch up around your toes in a painful knot. Suddenly the steep hill will end and the G's increase as you change vector, running along the now flat plane of the world.
Stand at the bottom of the hill and gasp for breath. Review the path you took. It's amazing. The speed and the danger. The strength and the courage. The luck of the gods.
Since I have gotten older, I have found a safer way to simulate this feeling. I have a dog. He likes to run. I put him on a leash and encourage him to go. I run behind the dog and let him pull. I take great leaping strides as the dog tears hell out of pavement with his two-foot long legs. A good dog will give you a nice steady burst for about 30 seconds, and wont screw you over by suddenly changing course.