When we think "young", we often associate the term with concepts such as flexibility and adaptability, learning and growth, energy and enthusiasm, and open-mindedness and bias for change.
However, as young people, we know that from a certain age onwards, these attributes are not simply given. It is not because we are in our twenties that we are energetic, open to learning and constantly thirsty for the next challenge. This energy and attitude becomes something one must work on through regular practice. A 70-year old, and there are countless examples of this, can be many times sharper and more lively in his or her brain than a 20-year old who is supposedly in the peak of youth, in the best years to challenge body and mind through personal initiative.
I think youth in body and mind are a function of (ideally, daily) consistent practices that take us on a continuous upward path. The end being so far away helps us realise how undeveloped we still are. Now, this has to be taken in with humility and excitement. It is an opportunity! It is an offer for self-exploration and new adventures. The practices that allow us to remain in such a "state of youth", as characterised by concepts mentioned earlier, abound. Different people preach different practices for constantly improving, usually to be performed daily, and all are as exciting: reading books, meditating, exercising, having challenging conversations and so on.
Cicero declared: "It is exercise alone that supports the spirit, and keeps the mind in vigor".
I suggest, though emphasising it is by no means the only factor, that consistent physical activity, be it dance, long-distance walking, basketball or weight-lifting, keeps your body and mind sharp. Its regular practice instils discipline, perseverance, and humility. Through exercise, one meets the body's limits, and if willing, learns to push these limits further and further. The beauty of this growth trajectory is that it is never-ending. There is always space for betterment. There is always space for creativity and new approaches to take the body's abilities a step further. When regular physical activity is taken seriously, the body remains young (within the limitations of age and decay, of course!): its curiosity and relentlessness in exploring itself allows it to remain open to growth and learning.
"If you always put a limit on everything you do, it will spread into your work and into your life. There are no limits. There are only plateaus, and you must not stay there, you must go beyond them." - Bruce Lee once said.
Indeed, what you do in you regular physical practice does not stop at the physical level. The benefits of consistent physical practice permeate the realm of the body and can lighten up our minds like we have just been pumped with the energy of life and youth. It touches our life at large. First, through the chemical processes that occur which keep our minds healthy and young. Second, through the habits of discipline and through the openness to challenge and hardship built during exercise which often give us momentum to grow in other areas of our lives: spiritual, emotional or intellectual.
"It's a way of life that teaches you better skills", Jennifer Hudson very wisely said.
I have experienced this over and over. I have gone through ups and downs in my regular physical practices. Many of the liveliest, “sunniest”, most refreshing and exciting periods of my life have been brought about and enabled by the physical and emotional transformation that challenging physical activity drives. Therefore, I have chosen long ago to take my youth into my own hands and sweat it out as often as possible!