I thought about it some more and the relevant question is - how do we guess what are his abilities? And what is his aptitude at those abilities? Is there statistical methods we can use? (e.g. SPR) What would the outcome be? How can we deduce his utility function?

Normally, when one has e.g. high mathematical aptitude, or programming aptitude, or the like, as a teenager one still has to work on it and train (the brain undergoes significant synaptic pruning at about 20 years of age, limiting your opportunity to improve afterwards), and regardless of the final goal, the intelligent people tend to have a lot of things to show from back when they were practising. I think most people see absence of such stuff as a very strong indicator of lack of ability, especially as seeing it so provides incentive to demonstrate the ability.