Exercise.
Moving your body is beneficial for your physical and mental health. Exercising consistently will not only add years to your life, it'll improve your sleep and energy levels throughout each day. Studies find that exercising decreases symptoms of inattention and hyperactivity and leads to better cognitive performance. Even better, exercise comes in all shapes and forms.
If you're looking for something more relaxing, try yoga, which also has amazing health benefits. Have an itch for intensity? Head to the gym and lift weights or you can do calisthenics wherever you want. Swimming is easy on the joints, hiking helps you connect with nature, and running is a gold standard cardiovascular activity. With all of these benefits, there's no reason that you shouldn't be exercising.