It's never too early to comprehend and acknowledge the fact your time at this circus is finite. I'm not saying you need to dwell on it day in and day out, but you won't achieve a realistic perspective until and unless you understand you'll be exiting at some point - with or without any closure you may have wished for.
As to the "first to die" bit ... This same sort of speculation emerged within my closest circle of friends as we entered our fifties. I would often pose that question as a deliberate opening gambit for discussing how one or some of us might be working too hard to hasten the end (e.g., via self-destructive habits). At least two of my closest friends finally took steps to clean up their act after I repeatedly needled them to the effect I expected to attend their funerals sooner than for other close friends. It provided something of a challenge they took to heart and acted upon.
As soon as you feel you've attained the situation / status that will be in force for the remainder of your life it's reasonable (I'd say wise ... ) to consider who and / or what you can expect to leave behind. If there's a certain way you'd prefer things to play out once you've left the stage, you need to ensure that outcome.
Death where is thy sting? Out of sheer stubbornness I will stay until God or the Devil claims me - but there are losses worse than death. In any case, I've always lived by the motto 'Ye knowest not the day nor the hour' - Indeed I used to have it printed on my mug. Once I've gone I've gone - let the chips fall as they may.
Edit - Maximus, I also am 64 , by one day now.
Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.
Though wise men at their end know dark is right,
Because their words had forked no lightning they
Do not go gentle into that good night.
Good men, the last wave by, crying how bright
Their frail deeds might have danced in a green bay,
Rage, rage against the dying of the light.
Wild men who caught and sang the sun in flight,
And learn, too late, they grieved it on its way,
Do not go gentle into that good night.
Grave men, near death, who see with blinding sight
Blind eyes could blaze like meteors and be gay,
Rage, rage against the dying of the light.
And you, my father, there on that sad height,
Curse, bless, me now with your fierce tears, I pray.
Do not go gentle into that good night.
Rage, rage against the dying of the light.