This information is from a peacock fact sheet:
"Full grown chicks of both genders are identical to their
mothers until about six months old when the male’s cream
coloured chest feathers start to turn a blacky-blue colour.
This is usually the only way to tell a male from a female
chick. From this point on he will continue to turn blue but
will keep his tiger-striped back and train feathers until about
two years old when they start to turn green. At about three
years he will begin to grow eye feathers but may take two
winters to grow full length eye feathers. It is very difficult
to determine the gender of white peafowl since this colour
change does not occur. You may have to wait until three
years old to see if the bird grows a train, in which case it is
a male. The only other clue is the length of legs, and size
of spur. Males have longer legs than females, and females
don’t grow large spurs."
Fact sheet is found here:
http://www.uwa.edu.au/__data/assets/pdf_file/0015/114153/peacock_info.pdf
Hope that helps!