The best exercise for a 50-year-old depends on factors like their current fitness level, health status, goals, and preferences. However, here are some exercises commonly recommended for individuals around that age:

Walking: It's low-impact, easy to do, and can be adjusted in intensity based on fitness level.
Swimming: Another low-impact exercise that is gentle on the joints while providing a full-body workout.
Strength training: Incorporating resistance exercises using body weight, free weights, or resistance bands can help maintain muscle mass, bone density, and metabolism.
Yoga: Improves flexibility, balance, and can help alleviate stress and promote relaxation.
Cycling: Whether outdoor or stationary, cycling is great for cardiovascular health and leg strength.
Pilates: Focuses on core strength, flexibility, and overall body awareness, which can help prevent injuries and improve posture.
Tai Chi: This gentle form of martial arts improves balance, flexibility, and mental clarity.

Always consult with a healthcare professional before starting any new exercise program, especially if you have any health concerns or conditions. And remember to start slowly and gradually increase intensity to avoid injury.