I no longer do centuries, but then I'm only 82 years 'young' and still ride 100+ miles a week year 'round.
Have done well over a hundred centuries and 6 double centuries.
As for 'hiils' . . . have ridden central Florida and hate to call those things 'hills'!
Most hill work I've done is 22,000 feet of climbing in 325 miles of riding in 3 days and finishing that event at 103 degrees; but I was 25 years
younger then! Oh, and did that on a tandem bike with my wife.
So go out and do your next century . . .