Question: when did we find out samus was a girl
Answer: the end of the game

title: Samus Aran
text: "Metroid", Gunpei Yokoi, took advantage of this shortcut. The series' co-creator Yoshio Sakamoto recalled, "We were partway through the development process when one of the staff members said 'Hey, wouldn't that be kind of cool if it turned out that this person inside the suit was a woman?'" The developers voted on the concept, and it passed. The game's instruction manual refers to Samus as if she were male to obscure her real sex until the end of the game. Sakamoto noted that during the course of the "Metroid" series, developers constantly try to express Samus' femininity without sexually objectifying