This song could either be taken literally or it could be taken to mean something like a grandparent looking at his/her grandchild growing up in a cruel world that is unlike the grandparent's childhood world and he/she remembers how it was good to be young when times were good, but now the bliss is over and "the green leaves of summer" (which may refer to heaven or a return to happier times) are calling the someone away into a peaceful resting place after death.
This song could either be taken literally or it could be taken to mean something like a grandparent looking at his/her grandchild growing up in a cruel world that is unlike the grandparent's childhood world and he/she remembers how it was good to be young when times were good, but now the bliss is over and "the green leaves of summer" (which may refer to heaven or a return to happier times) are calling the someone away into a peaceful resting place after death.