Zoom in and you will be able to see pointy saddle feathers coming in.
Also, at 10 weeks old pullets would not have such big and red combs and wattles.
I have had ISA browns that had serious comb and wattle growth at a young age, but I admit, not that much. I still believe that IF the red bird is a "pure" Red Sex Link", it's a female (although almost all the others being mixed points that it's mixed). If the Red bird is a mix, I agree, it's a cockerel
I can't seem to be able to see the saddle feathers, but it would not be the first time my eyes fail me