Whether it's Big Mama or the female Predators of Hunting Grounds, most tie-in media proposes that female Predators exist - it's just that the films never showed them. This is all fan conjecture since AFAIK the production staff never discussed anything like this, but could the films already have shown both male and female Predators?

There appear to be two core design archetypes for these creatures. The first type features dull and mottled coloration, a wide and smooth cranium with a single crease down the middle of the forehead, and a preference for stealthy, careful, and strategic combat. This encompasses the Jungle Hunter and Scar, as well as both Elder Predators (whose facial quills seem to begin sprouting with advanced age). This cautious and observant nature could also account for these Elders surviving for so long.

The second type has a prominent row of blunt horns which frames the edge of their cranium and a more complex, stitch-like forehead crease. They seem to have much more vivid coloration, but this dichromatism appears to fade with age (as Wolf was designed to be "middle-aged"). Their temperament is more aggressive and favors direct conflict, diving directly into encounters in which they have a significant disadvantage (City Hunter trying to fist-fight a heavily armed Harrigan, etc). Whereas the Jungle Hunter stalked primarily to separate and pick off members of Dutch's team until only the strongest survived, the City Hunter appears to stalk Harrigan mostly to torment and provoke him.
This dimorphism suggests to me that most of the Predators we see in the films are female, with the City Hunter and Wolf being the only two males. How this relates to newer Predator designs like Feral (who exhibits traits of both "types"), I have no idea.

One last theory is that the tiny (and incredibly unimpressive looking) skulls that Predators adorn themselves with are relics of their youth. Predators appear to share many traits with terrestrial reptiles, so abandoning their young is a distinct possibility. Could these skulls be trophies taken from creatures that prey on newborn Predators? These decorations might display the earliest victories of the infant Predator as it struggles to survive to maturity.
Of course, a Predator's anatomy isn't going to be directly analogous to the genders or characteristics of any lifeform we know because it's

so who knows.