David Palmer's Qigong Fever is a very good scholarly account of qigong. In it, Palmer argues that what we now know as Qigong emerged in the 1950s as part of a public health campaign initiated by the Chinese state. That isn't to say that qigong was invented in the 1950s - various aspects of what we know as qigong have been a part of martial, religious and healing traditions for a very long time. In the 1950s, these various disparate elements were systematized into a coherent whole. The first book published using the term qigong was Liu Guizhen's 1957 Qigong Healing Methods.
Chinese martial artis I've spoken to who were alive at the time have told me that nobody called it qigong before that time. The Chinese martial arts, and Traditional Chinese medicine also went through a process of systemization during the early 20th century. As with qigong, they're neither new nor ancient - the old was reformulated in modern times.