I was just introduced to this expression last night when I questioned my daughter how could 23 years of human life be "her time"? How could there have been nothing else for her soul to do in this lifetime?
It was explained to me that we in human form live in a three dimensional world, so our mind is conditioned to a time, place, space continuum. However, in Spirit there is no time. Therefore, the expression "it was their time is inaccurate although understandable.
What is Season of the Soul? A Soul that leaves it's physical form at age 95, as a young adult at 23, a child of 8, an infant at 15 months or a fetus at 26 weeks or a "Stillborn" baby or an infant that dies through "SIDS", these Souls have all completed that Season of their Soul and left those physical forms.
You cannot "die", the Soul cannot, will not, leave the body if the Season is not complete. A person cannot "'Soul Destiny' themself to kill themself". That means that if the Soul Season is not complete, a Soul will not leave the body even through Suicide.
The Soul chooses how it will depart from the body. Yet, it pains the human parent deeply, how their child, this beloved Being, did leave their body. In the human realm there is so much stigma, and judgment about it all especially with addiction and suicide. Yet please know , none of this defines the greatness or beauty of this precious Being called your child. Let yourself not feel dishonored by anyone's opinions or judgments for they cannot unless you allow it.
Let yourself know that there is Divine perfection in all, even though we cannot fathom so. In that is our own judgment, our own arrogance about what is or is not in the Spiritual Realm which we cannot possibly know the Truth of.
In this lifetime experience the Soul, your beloved, completed all that It came here for. Your loved one has left the physical body which served It to be in the physical Human Realm, and has gone back to the "Source of All" which is "Home".
There is no Death as humans think of it. The Soul never dies. There are only Seasons Of The Soul.