64 and just a few weeks shy of 65.
Quick "age" story. My grandfather, born in 1907, said he was considering one last canoe trip in Minnesota or Canada, this when my brother and I were in high school, so in the late 1960s. He'd have been just over age 60. "Poppy" had beguiled us with stories about canoeing across one lake, then a portage, then another lake, then another portage . . . through an endless chain of lakes like a bead of pearls. My brother and I looked at him like he was crazy. An old fat man carrying a canoe on his head between lakes? He corrected us, said a man in his late 50s, even 60s could make such a trip if he were prepared. It never happened, but it stuck in our minds.
Fast forward to 2017. We are both older than Poppy was then. Randy, 63, just got back from New Zealand where he placed 3rd in the World Masters Weightlifting Championships; and, I take off to Baton Rouge in July, one week before my birthday, to compete at the Masters Nationals Track & Field Championships in the 60 to 64 age group. I'll be the oldest dude in my class just missing the 65-to 69 age group. But, I'll have lots of fun.
My, my . . . how perspectives change from teenagers to "mature" men.
I should note that people today in their 50s/60s/70s and so on DO seem a lot younger today, act younger, than back then. No doubt about it.
I'd say someone in reasonable shape should be able to kayak well into their 70s, maybe even 80. You just have to moderate your expectations a bit and be more careful.