I just turned 76, but am experiencing some of the things you mention. I saw a specialist last summer, and I'm not imagining it. The doctor gave me instructions to become more socially active, which is not easy for me as I'm an introvert. (I joined a quilt guild.) He suggested exercise 150 minutes a week, including walking and to do intellectually stimulating activities. I am doing more crosswords and reading more.
My friend suggested doing an online brain stimulator, which sounds like torture to me, but he enjoys the challenge of it and feels like it has helped him. Apparently, it does something that you have to respond to. If you are interested, I'll get the details from him.
I know I tend to sit in front of the TV when I am tired, but I am making an effort to read instead.
Good luck.
bkay