Kungfu and Tai Chi are both considered traditional Chinese culture essence.
As martial art, Tai Chi is soft internal style exercise and focus more on breathing, Chi's flow and relaxation, it's more suitable for adult. Kung Fu is hard external style and typically more concerned with developing athletic skill sets and liked mostly by young people.

No matter which style you practice, the training all emphasize on body's coordination and high degree of mind concentration. Continuous years' practice develop body's integrity and free flow of internal Qi (energy).