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I'm leaning boy, but as he's only five and he's a marginated, it's hard to say. I definitely thought my big lady Gino looked like a male up until the day she started laying infertile eggs. Marginated tortoises are ridiculously difficult to tell. If he's behaving in an inordinately aggressive manner toward his pen mates (if he/she even has pen mates), this would be another piece of evidence suggesting male. Also, if he has an elongated head, he is most likely male. Most female marginateds I've seen have comparatively short heads. I don't know why this is. But yes, too young to tell 100%, but it looks like a boy to me.