Yep, I feel this. I'm 59 and a regular fitness enthusiast (former and maybe future competitive runner/triathlete) and I've weighed the same for decades, no matter what I ate. Only in the last few months have I noticed that my weight fluctuates more--and I'm seeing higher highs unrelated to massive meals or sedentary days. I haven't yet started any calorie-counting, but I'm cutting out late snacks (after 8PM) and trying to eat earlier. I guess the meta- in metabolism is all about change!

Great piece. And good luck!