buddhist/hindus believe in a system of reincarnation - which states that we are reborn upon death.
who we are reborn as depends on how well we complete our Dharma - or as it is known in christianity as a "calling."
through seeking enlightenment - life after life - eventually a person can transcend earth and the cycle of rebirth.
for those who believe in this - they would explain that "past lives" are real - and that feeling you get is the residue on your soul from a previous life.
christians do not believe in this. they believe you have a soul - and when you die, if you accept jesus, you go to heaven...
otherwise, if you do not repent, the jealous god sends you to hell for all eternity.
i personally have met young people with maturity and wisdom far beyond their years...and i look at them and wonder if they are an "old soul."
i have also met some childish old people (like opinionated) who make me think they are "young souls"
but if this old and young soul system is in place...how are souls created? how are they destroyed?