I'm 66 and do a few triathlons each Summer. Each race, there are only a few of us old geezers that participate. If you look at the national triathlon performance statistics for each age group, the 55-59 age group is still very competitive. Slightly less so for the 60-64 group. Performance drops dramatically for the 65-69 group. If you than look at each disciple, swim, bike, run, it's the run that seems to slow down first.

I know from my own experience, I'm still improving my swim times since it's VERY technique dependent. I've been a life long cyclist so I still feel strong on the bike and do most of my passing on the ride. My running, no matter what I do doesn't seem to get better. If I run to much, I need additional rest days to recover.