I find that a number of posts have had questions about Century types.
Perhaps I can summarize them
Personal Fast Century: A ride of a hundred miles in which you attempt to exceed your personal best.
Fast Century: A ride of a hundred miles in which you complete in 5 hours or less.
Organized Century: A ride of a hundred miles with a group of other riders usually with designated rest stops and supported by a van/truck in the event of a break-down (of you or the bike )
Unorganized Century: A ride of a hundred miles with or without other riders. It might have a support vehicle.
Solo Century: A ride of a hundred miles usually without other riders or a support vehicle.
Scenic Century: A ride of a hundred miles which has several stops, picture taking, talking with people along the way, smelling the flowers, lunch, etc. Usually it takes ten hours or more.
Some of these Century types overlap. For instance your century could be a Personal Fast Century, Fast Century, Unorganized Century and Solo.
All of these are bona fide Centuries, but not everyone can complete every one of them.
The question comes when a given rider (esp. a Newby) asks if he/she can complete a Century. And a forum poster will assume one type of Century and advise for or against doing it. In my opinion, a Newby with some previous experience of 40-50 mile rides can usually do a "Scenic Century" and possibly an Organized Century; but a Fast Century is not advisable.
Personally, I enjoy my solo, scenic Centuries. I ride them for fun. I like stopping at a fast-food outlet, ordering a burger, and chatting with other patrons. I like taking pictures of old cars and old houses along the way. I don't begrudge the fast rider who polishes a Century in half the time; but I enjoy riding 15-20 km/hr (10-13 mph) average.
A Century should meet your personal goals -- not just your speed goals.
Enjoy your ride.