Just want to add something that I don't think was mentioned yet.
Ride with a friend, or make one on the ride
I can say after my first century that I rode the first almost 2 hours pretty solo, or tailing on the end of some groups that were a little too fast for me (I would fall off and wasn't going to ask them to slow down). But once I got in a group that was pacing at a reasonable pace (IMO) and got to chatting, the next several hours flew by and the ride was 150% more enjoyable.
Excited to ride centuries outside of organized events, but also very excited to ride with some folks, makes it all the more enjoyable and allows you to keep a pace that you know is acceptable because you can talk and not huff and puff the whole time.