Man, I have to delve back into prehistory to remember some of the early century rides.
Still, a lot of solo rides.
I did a couple of bike-a-thons as a kid, but I think they were about 80 miles or so. I think I finished, but I can't remember for sure. One of them I was riding the old 24" 5-speed (Gitane?) which would have put me around 6th grade. I can remember getting a flat, and the tire being a major hassle to repair. I think with the help of another rider, we did get it repaired and I got back on the road.
In the early era, we did a few rides with my parents from Creswell, OR to Riddle, OR. Not entirely straight, so 100 or so miles, perhaps more. But done in 2 days with a layover in Roseburg. At least one hill had spots of gravel.
Now there was a ride as a late teenager, I think, when I went riding with my parents on Century Drive in Eastern Oregon. Then I camped overnight and I rode back home to Eugene, via Sisters and the McKenzie Pass. As it was getting dark, I called my parents for a pickup around Leaburg. Probably a total of about 100 miles by bike that second day. The McKenzie Pass is much easier from the East than the West, but still, it was a good ride, carrying camping gear.
Fall of 1986, I did my "Megameter" ride. Studying in Italy, I decided to ride from Parma, Italy to Rome, Italy, and back, to get my passport renewed. 10 days total (including about 3 days layover in Rome), and about 1 megameter. I got down to Rome, and they refused to renew my passport because I was staying in Parma and was supposed to go to Milano (nobody cared that I had just ridden my bicycle several days to get to the US Embassy in Rome). I can't say for sure. I think several days were around 60 miles, but I may have hit a couple of days of > 100 miles. Abetone was > 1 mile of climbing. I also broke my bike rack on that ride. I had it re-welded in a small town near Pistoia, and made it almost back to Parma before it broke again, limping the last few km back to Parma with a broken rack.
Spring of 1987, I rode most of the way from Parma, Italy, past Venice, and up towards Grado. I didn't make it all the way to Grado before catching the train, but made it close. It was a mighty long ride. I had estimated it was near 150 Google says it is about 222km from Parma to Venice, and I was a bit north of there.
My first "Official" Century would have been the "Reach the Beach" ride in the early 1990's. I think it was about 150 miles from Monroe, Oregon to Amity, Oregon to Lincoln City, Oregon. I was going to have some friends with me, but they all bailed. That is perhaps the only century ride that I actually specifically trained for. I actually started in Springfield, OR, putting the ride closer to 180 miles. Whew, I was toast when I arrived at the finish line. Well, I was pretty well shot for the entire final leg from Amity to Lincoln City. Then, since it was a 1-way ride, I camped overnight, then turned around the next day, and made my way back home (taking a few shortcuts).
I did 2 marathons, and the Hood to Coast running relay in the late 90's, but don't remember any century rides.
Early 2000's, maybe 50 or 60 mile rides in Missouri, some on the Katy Trail.
About 5 years ago, after quite a dry spell, I went "car-free" (driving again now), but I did several rides back and forth between Eugene and Portland, ranging from 130 to 200 miles. I did the "Blackberry Century" twice. And, tried to ride from Eugene to Crater Lake (got almost to Diamond Lake the first day). I completed the ride in 4 days total, for a pretty intense few days, and a lot of climbing.