Something that Magnus made clear once about why you can only become a top GM if you start early, is that children process information differently.
For a young child, chess becomes their life, as opposed to an element within their life.
The brain as such attaches affinities to things that happen on the chessboard vs. things that happen in the realm of family, school, going out, etc.
This is why superGMs can see things no one can - they have emotional weights added to the visual and cortical information they're receiving. And in comparison, adults can only learn chess the robotic way-like it's a school subject- because their emotional attachments and affinities have already been formed.
There's hardly any adult who will 'emotionally' care about his C-knight, you see.
But to a top GM that knight may be more important than his parents. So maneuvering that knight is a matter of life and death, and not just part of a game. Adults 'know better' but that's why they don't make it as far. We would have to be entirely rewired. Do LSD until only pure unfiltered reality enters the brain, you have forgotten everybody and everything, and then start with a chessboard 
The truth is harsh.
I think the reason so few people reach top level chess after learning at a late age is not because of lack of talent, or lack of money, or lack of dedication, or lack of resources.
I think the reason is because if someone wants to start chess at age 25 (or more) and is willing to spend the hours, dedication, money etc just to become a grandmaster, that goal alone tells me they are not smart enough to ever become a grandmaster.