Have U or your mom asked the dr. to let him stop for awhile to see if things get better? I really hate it when drs. blame things on "age", especially at only 61. His problem could very well be the statin, as memory loss is a side effect. Seeing he does construction work, memory loss is definitely something he doesn't need, could be dangerous.
My hubby was on Lipitor for 7 years, had many side effects, especially muscle weakness and pain. We didn't have a computer at the time so I had no idea what some of these drugs can do, but sure do now. Due to his ailments he had to retire in 99, 3 years short of when he intended to. He no longer takes any statins, and both of us refuse to, although there are folks who do well on them, many don't.
Sounds like U are a very nice and concerned daughter, and think it is time for a talk with his dr. Seeing he is maintaining decent numbers, a lower dose may be just fine for him. My neighbors dad was on Lipitor and as soon as his dr. saw a decent improvement, he kept lowering the dose till everyone was happy, so it can be done.
I wish U and the family alot of luck, and hope it all turns out well...