The ultimate acceptance of mortality is only achieved by the personal dissolution into a larger, collective existence. I love this philosophical exploration of aging and personal growth by Bertrand Ressell.
I think that a successful old age is easiest for those who have strong impersonal interests involving appropriate activities. It is in this sphere that long experience is really fruitful, and it is in this sphere that the wisdom born of experience can be exercised without being oppressive.
It is not us telling grown-up children not to make mistakes, both because they will not believe you and because mistakes are an essential part of education. But if you are one of those who are incapable of impersonal interests, you may find that your life will be empty unless you concern yourself with your children and grandchildren. In that case, you must realize that while you can still render them material services, such as making them an allowance or knitting them jumpers, you must not expect that they will enjoy your company.
Some old people are oppressed by the fear of death. [..] The best way to overcome this fear—so at least it seems to me—is to make your interests gradually wider and more impersonal. Until, bit by bit, the walls of the ego recede and your life becomes increasingly merged into the universal life. An individual human existence should be like a river—small at first, narrowly contained within its banks, and rushing passionately past boulders and over waterfalls. Gradually, the river grows wider, the banks recede, the water flows more quickly, and in the end, without any visible break, they become merged in the sea and painlessly lose their individual being.