Complex sentence: During the Cultural Revolution (1966--76) Shen, already in his 80s, was tortured by the young Red Guards who were against all non-communist forms of art and culture and declared him a "counter-revolutionary".
Split into simpler sentences: During the Cultural Revolution (1966-76) Shen, already in his 80s, was tortured by the young Red Guards. The Red Guards were against all non-communist forms of art and culture and declared Shen a "counter-revolutionary".