I'm doing my OU Masters in Maths now, in my 40s. It is definitely hard, but I'm enjoying it. Personally I struggle to learning things thoroughly unless I'm working in the subject, or I have exams to do. My own learning workflow is to flip through a chapter to get an overview, then read/re-read it thoroughly, then go through the exercises on the chapters quickly looking at the answers. Read the chapter again, then try doing the exercises without help.
I've found YouTube pretty good for getting the intuition behind some ideas.
Be careful with the direction of causality here. It may be that giving up his hobbies hastened his dementia, OTOH it could easily be that the onset of his dementia led to him giving up his hobbies.
He links to a Woodford Investment analysis that states that Brexit might not be that bad for the UK (the report is from Feb 2016). This goes against every other analyst report that I've read, and the optimism seems to be based on a perception that doing trade deals with other countries is easy. My guess is that the author is a Brexit supporter looking to justify their position. "Oh, I voted with all the old people? They are all actually really wise".