If you significantly out live your initial assumptions then it’s likely not to be in one piece. How many physically and mentally fit 95 year olds do you know for example?

Just make sure you live in a country which will look after you if you lose your mind in old age and plan a withdrawal system that allows you to live during your assumption period perhaps?

Finally if that’s too dark then take an insurance policy with a payout for a long life, in simple terms make a bet that you will live a long time and then cash in if you do to fund that period that you did.