I've never believed people who said that as you get older your metabolism begins to slow down and you gain weight. There were times in my 50s when I was much more active than when I was in my 20s and yet I had trouble keeping my weight down. No, I think (besides the obvious that you may eat more) that you gain weight because you're more efficient.
Think about it, you're older, you're wiser. You may have more to do, so you plan your time better. Instead of, say filing one piece of paper, you wait until you have several. Then you pull a chair over to your cabinet and file your papers. If you were filing one piece at a time, think of the walking you could be doing.
When I lived in Queens, I had a two story house. I did what all the "experts" said to do. Instead of making several trips upstairs to put things away, I stacked them on the stairs and brought a bunch up at once, thereby saving several trips and not burning calories.
It's even worse here with everything on one floor. I empty the trash baskets all at the same time and bring it to the garage all at once. How much more exercise would I get if I emptied one basket at a time and brought it to the garage.
Hmm, I think I'll try this. How many calories will I burn by hanging my clothes in the closet, one piece at a time?