I’m 51 and seeing my best fitness due to additional volume and more focus. The ceiling goes down every year, but very few amateurs are up against their ceiling.
I’d also say that Leadville leans heavily on endurance and nutrition. Critical that you can hold a high percentage of ftp for 8+ hours, actual ftp is just a starting point. I’m a big believer in doing a few 5-6+ hour rides w/~300 tss each month to really push the endurance.