There are very clear differences between hens and roosters at 2 to 3 months of age. The most obvious signs that indicate the sex are:
Rooster (Male)-Larger comb, larger wattles, and the most obvious is the tail feathers. A young roosters tail feathers will be more disheveled looking and pointier than a hen's. A young roo may also be developing small nubs on his ankles.
Hens (Females)-Small comb, smaller wattles, and rounded tail feathers. See video and more below.
Rooster (Male)-Larger comb, larger wattles, and the most obvious is the tail feathers. A young roosters tail feathers will be more disheveled looking and pointier than a hen's. A young roo may also be developing small nubs on his ankles.
Hens (Females)-Small comb, smaller wattles, and rounded tail feathers. See video and more below.
Featured Video: Differentiating 2-3 Month old hens from Roosters
This video was made when the hens were about 13 weeks old and the roosters were about 14 weeks old.