The soul is like a drop of water that is part of the vast ocean of consciousness we call God, 'All that Is' or any divine name you like. This ocean is the creative, expansive force of the universe, an energy of unconditional love and infinite possibility. Yet a very tiny part of that droplet is actually in possession of our body and human consciousness; there is a large part of the soul that holds awareness in higher realms. So we have a tiny piece of soul energy inside of us, sometimes trapped in illusion and old patterns, and the larger part of our soul is dancing in the cosmos. We call that part the higher Self.
Soul in and of itself is perfected because it IS 'God' not just connected to God. When we talk about soul growth, we're not really talking about the soul growing, it's really about seeing, integrating and releasing the karmic patterns and illusions from previous incarnations so the soul can embody more fully and with greater clarity.
When we embody our soul or higher Self we know who we really are at a deeper level and we can feel as if we're observing our personality parts and patterns rather than being wholly identified with them.
As for the soul in astrology, no one can know the consciousness of a person from the chart. A lot of people are born at the same moment, plus a lot of puppies, kittens and termites. A conscious soul can work with the energetic possibilities seen through the astrology chart, and can integrate and work with the higher frequencies of each planet more easily. The less conscious soul is more likely to experience difficult events in order to grow. This really explains why many old astrology texts concentrate on negative meanings and dire predictions and newer forms of astrology such as evolutionary astrology or humanistic astrology are more co-creative and empowering.
An example would be Neptune, our capacity for divine love, oneness and compassion. This of course sounds very spiritual, and a person with a strong Neptune or lots of planets in Pisces could be very spiritual and seem like an old soul. Yet a less conscious soul could have the same chart and be more connected to the other qualities of Pisces and Neptune: illusion, confusion, deception, spaciness and various kinds of addictions. Somewhere in between we find caring for the less fortunate, transcendent art, music and film making. Throughout a life most people will experiment with many of the possibilities shown in their astrology chart, hopefully finding a way to be authentically themselves.
So, it's not the chart; it's what you do with it. The choices are always there and your soul is always with you, reminding you to live life fully.