Here's the oldest Rainier climber I've been able to find so far, from a 2006 article on a Mt. Rainier website:
"So, what will YOU be doing at age 83? If you're Bill Painter, you're still climbing Mount Rainier. Mr. Painter of Richland, WA successfully ascended the Kautz Glacier route this weekend with his family and friends.
He described the climb as his "most technical so far," but when I asked how he was feeling afterward, Bill's response was, "I feel fine today, but I sunburnt my lip a little." For training, Bill (a self described "family man") rides his bike at least 100 miles each week and regularly hikes a local hill called Badger Mountain... Actually, he makes that hike quite a bit... 1,502 times to be exact. But most of all, he credits his fitness to a life of hard work. Congratulations, Bill Painter!"
Heck, I'm a youngster compared to that guy! And I have a very similar training regimen (except for a lifetime of hard work, I've always been successful at avoiding hard work!)..... "Use it or lose it, baby!" Here's a picture below of the old boy himself....orange helmet, and then me in a black hat! I think I'm much tougher looking, huh?