Since you brought up the issue, I will delve more into it.
When we are born, and as children, we do carry an emotional, mental and spiritual baggage from "past" lifetimes. (simplifying this, as time is parallel). So in this sense, the personality is not a clean slate at all!
As children we are full of trust, confidence and joy because we know that we are alive, we exist as conscious creatures, and we are eager to continue our journey towards enlightenment (a journey we have begun many lifetimes ago).

experiences we live through, this soul is filled with negative and useless things?

Not the soul, but the human personality. The soul remains intact. It is free, non judgemental, and full of joy. It's the adult human who is filled with mass consciousness which is afraid, not trusting, depressed, hopeless.

I hope it's clearer now. Please ask if not.

in the case of the elderly, is there a channel of enlightenment and love for them?

Enlightenment is ageless. In fact, many people are connected with their soul self in their old age more than they are as mature adults because they finally allow themselves to lower the shields and the protections that have blocked the other realities.