You loose ~30% of your neurons in the first ~2 years of life as you decide which neural networks to set up. Then you spend the next 25 to 30 years to decide how to set up your synaptic branching and the order of hierarchy. It’s down hill from there. You do gain wisdom and knowledge (they’re two very different things) and there’s a fair bit of neural plasticity that allows you to pick up the slack. But like so many neuro degenerative diseases AD is just another one where the basic problem is you don’t take out the garbage ( tau and amyloid) as quickly as you make it. Like atherosclerosis, arthritis and other degenerative diseases it’s a life long process. Some people are put together better (genetics). Some people stress their structures more (nature of work, diet, toxins, lifestyle). So chimney sweeps get testicular cancer, bricklayers get arthritis in their hands and my vodka drinking 2 pack a day pall mall smoking paternal grandmother lives to 95 in her own apartment totally independently and as sharp as a tack.
People act from fear. Peoples don’t accept correlation is NOT proof of causation. People still pore water on houses when all they’re going to save is the foundation. Piss away your money on what you want. Please go back and study basic biology. Learn about how your mitochondria work. Learn about beta amyloid and tau protein. Then decide. A little knowledge is a dangerous thing.
Personally I’m very, very disappointed in our FDA. Biogen pulled a fast one. If you look at all the trials imho there’s no way their AD drug should have been licensed. But I’ll be standing first in line to get my malaria and dengue fever vaccines.