Number seven is very important number. Music has seven fundamental notes (vibrations), Light too has seven fundamental colors (rainbow colors), so does a human. In yogic tradition enlightenment is about opening up seven Chakras. It is also considered lucky in many countries. Therefore human evolution is a seven step journey in yogic traditions of India. Buddha was born in India/Nepal steeped in spiritual/yogic traditions. Walking seven steps is a metaphor which implies enlightenment (Nirvana) as the destiny of the boy.