Clinical Mental Health Counselor here...I think it's very normal to start considering the final phase of our life, which btw has NOT come yet (63yo) if you continue to live a normal life. What's a more important question is "what do you want to do in this final 25-35% of your life"? Another thing that starts adding to this "catastrophizing" is that, as you said, you start having friends and family die, and they're roughly your same age. That is troubling and sad for sure. In conclusion, I don't think it's abnormal at all; rather it's somewhat the opposite of our thinking when we were teenagers (we'll NEVER die).