Hmm - I feel like EndGame's wisdom would be useful instead I will take a sophomoric attempt to articulate what I see.
Metaphors are useful to help us understand but there is no literal 12year old boy or 23 year old sober man. When we abuse chemicals I believe we stunt our emotional maturity at that age. I believe this to be the case based on my experience. In many ways Rob you interrupted your normal aging process with the choices you have made along the way. Whether this was your decision or the result of the consequential decisions made for you by the cards you were dealt it does not matter, it happened. I believe part of this angst is the attempt to stitch together the patchwork quilt, which is now your life.
To use an analogy its like you got to college without understanding grammar and were taking a creative writing course but you lacked some of the basic fundamentals. You are ahead of your own capabilities in some ways based on drinking through your teens and then spending the next three decades sober.
I don't believe the boy is dead to go back to the metaphor because that personality, which the boy represents is part of you. We can't start compartmentalizing different traumas and timelines in our lives without developing dissociative personality disorders. We do this to survive, I have done this actually, but at some point the chickens come home to roost.
In my opinion much of the angst is often a result of what we are attaching our self identity to. There it is my view on attachment
This is often a challenge because if we are on a continuum in life then how can I be anything other than human? If I attach to my athleticism and I become paralyzed then do I still exist? Yes of course but I have to change my self identity rom an able bodied athlete in order to move forward. If I attach myself as an intellectual and develop Alzheimer's well you have to change that attached identity.
In many ways what I see occurring in your Rob is what I have gone through this past year. If has much less to do with sobriety for me but sobriety opened certain doors to walk down the halls of self reflections and the journey of who I am. This is so much more than leaving the drink and drugs, although that was the prerequisite, for me at least.
Hope some of these opinions based on my experiences might help.