I think it is pure speculation to say that we would become apathetic in as little as a few centuries, which to our current lifespan seems an unfathomable amount of time, but in the grand scheme of things is still exceedingly short. We might continue to develop further beautiful and fulfilling depth that is unreachable given the measly few decades of youthful energy we have today.
I spend a lot of my effort learning about and exercising my health. I’m wagering a bit of my energy now on catching the wave of advancing health and longevity research later. Some day I believe it will likely be possible for a person to ride this wave through extra healthy decades, catching scientific advances just in time to rewind their ticking clock by a few years, a few times or even indefinitely. It might be a pipe dream, but I think it’s worth a shot. If this doesn’t come true for me, I will at least likely have a longer than average healthspan.
I admit that perhaps the human brain and psyche have not evolved for happiness and fulfillment beyond our disappointingly short deadline. Still, I have to wonder whether the psychological disengagement and decay that we observe in many of our elderly would be different given prolonged health of body and brain.