You have a person who has an incredible talent, whether it be cooking, writing, sports, whatever. This person briefly showed this talent but then is living their life without fulfilling their calling in life. I would like a noun and I would hope it would not only convey that the rest of the population is missing out on that person's talent too.
Note: The Will Hunting comment is a good one. 1 out of 5 movies seem to be about this type of person.
Best Answer
Unrealized
As in, unrealized ambitions or aspirations.
It's not a noun but it describes the type of person who has wasted or thrown away an innate skill or talent.
If the OP is determined in wanting a noun to describe a person who squanders his/her talents; I believe many would label that person (perhaps too harshly), as being a loser.
EDIT: In lieu of the OP's comments that the person in question is neither lazy nor immature but on the contrary; a conscientious, devoted parent and son/daughter, the adjective, unrealized, still applies. If the dream was, for example, to be a singer but through circumstances beyond their control that gift failed to blossom. It is common to refer to that person as being an unrealized talent.
Finally, if one wanted to give a more positive and optimistic edge; one could define that same person as being undiscovered.