According to modern Western culture the answer is: To Stay Young; but given that is impossible, to pretend to stay young (by simulating a youthful appearance and behaviour).
(The only praise ever given to an older person nowadays is that they don't look or behave as if they are old - they seem almost asif they are young... They could pass as younger - in the dark, with the light behind them...)
There is, in fact, no alternative to this indirect condemnation of ageing - because from a secular materialist perspective ageing is decline, and nothing-but decline - and that's just a plain immovable fact about-which nothing whatsoever can be done.
For mainstream discourse old age is degenerative.
The real purpose of old age is spiritual - objectively spiritual - hence necessarily invisible to secularism.
In reality, old age - properly considered - is developmental (not degenerative) it is an unfolding of purpose. From one positive purpose to another...
The development from mature adulthood to old age properly includes the following shifts of focus:
From material to spiritual
From current to eternal
From elsewhere to here
From evaluating to knowing
From complexity to simplicity
From social to universal
From motivation to being
From creativity to comprehension
From speaking to praying
From listening to meditating
...Thus from commun-ication to commun-ion
From teaching to answering
And from answering what is asked - to answering what is needed.