Based off of several different surveys and research, it has been highly recommended that once adults become older, they should seek out activities that are not only mentally challenging but also novel.
For example, if you have never painted but also found it interesting, simply start painting. However, if you have painted throughout your life, then perhaps you should learn a new language or learn to play the piano. Traveling abroad to a foreign country is also another option.
The point is to seek out stimulating activities that are enjoyable and will lead to similar engaging experiences. Once you step out your comfort zone, you may never want to go back.