I've noticed that roos often develop feathers much more slowly than pullets in some breeds- but not all.
If those were my Orps I'd say the one with the long tail was a pullet and the rest were cockerels. You'll have to band her and see if it works out that way!
ETA- Our posts crossed! This is a good example, then of a breed in which it doesn't indicate anything, because I'm certain you didn't get all boys. I think the one is likely just a pullet who is a bit slow. I think SS are fairly reliable to sex by color and vent.