To me, the amount of feathering looks about right for being 2 1/2 weeks old.
Maybe there's a difference in brooder setup--chicks grow their feathers faster in some conditions than others. (Except for the chicks that just grow their feathers terribly slowly no matter how you brood them, clearly...
Is it the only lavender orpington you have?
Because some breeds develop combs much earlier than others, I feel more confident with guessing gender if I can compare several of the same breed and age.