The secret to youth is change. When you are young you are fresh and new. If you stay the same your entire existence, the world will adapt to you and you will cease to be new. A constant evolution will ensure you remain relevant.
If something always stays the same, it is inert. There is no life.
If circumstances cause it to move, it is lively, until the initial energy transfer has rebalanced.
The same goes for a person. One can be revitalized by circumstances, but eventually return to stagnation until influenced again. A reactive disposition. One can also become the source of one’s own volition and choose to act despite outside conditions. A proactive disposition.
As always, the ability to exercise both approaches would allow one to be fully adaptable to whatever may transpire.