Originally Posted by Iride01

It's very obvious that you can. My son even did his first century with me and rode the only bike he had at the time, a flat bar mountain bike 29er. A Trek Marlin weighing in at very heavy.

He saw the advantages of less weight and more aero on that ride. He got a Trek Emonda for the next century ride.

If you get a lightweight hybrid, you'll be better off than those on heavy hybrid if you wish to do centuries. But if you are performance oriented in your cycling, then consider the advantages of aero and being able to change up your hand positions on a drop bar which also changes the leverage of your body's ability to put power into the pedals for the times you wish to go very hard.

If you are not performance oriented, then the no-brainer should be that any bicycle or tricycle is acceptable. Just so long as you finish before the SAG time.