There were just 21 shooters in total that shot the minimum 6 shoots to qualify for the Nationals in 2015 in all categories apart from 'Open'. That's covering 2x junior classes, Ladies, Recoiling and 0.22. Ladies actually had the majority of those with 12 shooters.
If any shooter can choose to shoot in 'Open' anyway then what's the problem?
It seems to me to be a sport where flexibility and good eyesight are a major advantage, rather than physical strength. So ladies or shooters in their mid teens probably have no real disadvantage over other shooters. They probably have an advantage over shooters of a certain age, who's eyes are weakening and bodies stiffening up.
It's well known that women do well in standing air rifle. They actually have ( normally ) a longer leg to upper body ratio. This, plus their hip shape actually gives them an advantage when using the classic standing stance. The longer leg/body ratio also helps with kneelers.