STEPHEN IRA, a junior at Sarah Lawrence College, uploaded a video last March on We Happy Trans, a site that shares “positive perspectives” on being transgender.

In the breakneck six-and-a-half-minute monologue — hair tousled, sitting in a wood-paneled dorm room — Stephen exuberantly declared himself “a queer, a nerd fighter, a writer, an artist and a guy who needs a haircut,” and held forth on everything from his style icons (Truman Capote and “any male-identified person who wears thigh-highs or garters”) to his toy zebra.

Because Stephen, who was born Kathlyn, is the 21-year-old child of Warren Beatty and Annette Bening, the video went viral, garnering nearly half a million views. But that was not the only reason for its appeal. With its adrenalized, freewheeling eloquence, the video seemed like a battle cry for a new generation of post-gay gender activists, for whom Stephen represents a rare public face.

Armed with the millennial generation’s defining traits — Web savvy, boundless confidence and social networks that extend online and off — Stephen and his peers are forging a political identity all their own, often at odds with mainstream gay culture.