mjed, I love your theory, but I still think genetics play a bigger role. The amount of overhang, the frenulum tightness and glans size all contribute. These parameters in the adult guys cannot be fully predicted from their pre-puberty state. But you just get what was programmed for you. I was retractable early but fully covered when erect as a grown up.
I too remember as a young child easily being able to retract my foreskin even when erect and still ended up with a quite long foreskin that covered all the head when hard.
I have noticed that people who have a shorter foreskin usually seem to have much thinner skin than those with long foreskins like me, and also do not have much dartos muscles in the area between the outer and inner foreskin(the muscles that contract the tip of the foreskin closed). Some short foreskinned asians especially seem to have no dartos muscle at all so that their thin shaft skin transitions straight into thin, inner foreskin. You can often see these people also have a very thin skinned, loose scrotum (dartos muscles are what contract your scrotum into tight wrinkles when you are cold).
A foreskin with strong dartos muscle can contract ahead of the glans holding the foreskin in place, causing the foreskin to grow in tandem with the penis during childhood and puberty. A foreskin with no dartos muscles is not held in place ahead of the glans and so, without that constant force, the foreskin does not lengthen as the penis grows, first causing erections to expose the head, and then in extreme cases, leaving the foreskin unable to remain covering the head even when soft.