There is a lot of embellishment on the internet. But with that said, there are some very fast riders out there that can do a century in less than 5 hours, I am not one - got close a few years back when I was drafting a paceline machine on a pancake flat century, they spit me out after about 60 miles. I would suggest you find a bike club in your area, ride with the A group and then if you can keep your tongue out of your spokes you can post what ever speed you like. I have never been able to keep up with that group in our area - they are aliens.