"If a man does not keep pace with his companions,
perhaps it is because he hears a different drummer.
Let him step to the music which he hears,
however measured or far away.
"

-Henry David Thoreau (1817–1862)

This calls to mind that gifted kids can vary considerably from their chronological age peers, in reaching milestones.

Here is a roundup of common Behavior characteristics and early milestones which may indicate giftedness:
http://giftedissues.davidsongifted....p_of_traits_is_my_baby_o.html#Post248478