It's been a while since I fractured my ankle. My bicycle commute then was short and flat so I managed it even with a cast. But running, after the cast came off, I had to start all over again, and it took a while for my foot to loosen up enough to even do it. So I understand your frustration.

I'd postpone any centuries though for a while yet. Let your body tell you how it goes. When you are ready and the ankle feels good, then go find a century to ride. Mind you, I don't know how old you are, or how long the cycling season is where you live, so those will affect how fast you can return to doing a century. Your doctor may be able to advise.