I'm 57.
I was a distance runner in high school and college.
I eat like a pig, but I am very physically active to burn all the calories (and I have a high metabolism). I usually eat fairly healthy, but I don't really worry about that.
Most of my exercise now comes from mountain biking (a great full-body workout, especially in Colorado, where we have lots of hills and mountains). I also road bike and gravel bike and work out some with light weights. I don't run anymore due to hamstring and knee problems.
I hope I am still posting YouTube videos for many years to come (maybe not 40, but at least 20).