So much of the answer to this question depends on what a century means to you and how taxing you expect it to be based on your capabilities and how you approach the event.
For some people a century ride is just their normal Saturday. For others it is something they plan the entire season around.
Similarly - if you want to complete a century at a very aggressive pace that’s going to have you on your limit for a long time you should approach this very differently than if you’re going to take a break every 15-20 miles to fill up bottles and bellies.
Finally, do you intend to ride with a group that requires surging and hard efforts followed by relatively easy periods or do you plan to ride it closer to a time trial with a consistent steady pace?