Buddhist qigong originated from India’s Hatha yoga and pranayama (breath and energy control) tradition over 4000 years ago. It traveled into China through two main sources. First, it came to the Shaolin Temple (home of kung fu) in central China, where it was taught to Buddhist monks to make their bodies strong enough to withstand prolonged meditation sessions and stay healthy. The second source of Buddhist qigong is the Tantric tradition of Tibet, from where it spread throughout western China and moved eastward.
Qi-gong is essentially about aligning breath with specific ways of moving and is described as both meditative cultivation and physical exercises. In combination it ends up addressing strength, flexibility and energy flow in the body at the muscular, skeletal and organ level.
Budhist Tai Chi is rooted in qi-gong which predates it by a couple thousand years. Essentially Tai Chi is built on the foundation of the qi-gong.
What makes qi-gong suitable for everyone is its soft and gentle approach. All the movements and exercises are adaptable to whatever your needs are. To receive the enormous benefits from qi-gong will not take long after you have begun a regular practice. as little as a once a week class is sufficient. Obviously if you do more you will get even more benefit, but it needs to suit your life-style and routine.