Do you think this mindset could be from dealing with the aging process? For example, as we reach older ages, many parts of our lives are behind us and we may feel there's nothing left to look forward to so we slow down and lose interest in things.

I do agree with the idea of use it or lose it. I'm not sure what type of stuff you're trying to learn, but maybe you need something more challenging or with an added social aspect, like in a classroom or with a friend. I've heard that staying social is important for brain health as we get older.