"Old"

You may have been told that the best way to keep your brain healthy is to stay engaged in activities such as crossword puzzles and listening to music. But now we know that these sorts of “passive activities” may not be enough to boost cognitive function. Activities that are mentally challenging — studying a new language or picking up a new instrument — are more stimulating. And while these might be easier for younger people to pick up quickly, they’re certainly achievable by everyone else too! 
While youth confers some benefits, experience compensates with others. Emerging research suggests that certain domains of the adult brain retain a lifelong ability to create new connections, build new skills, and form new memories as you age. 
The takeaway: You’re only as old as you think you are.