I think this is trickier than just saying "do this, you obviously have time", but not for the reasons that derefr gave. I think you are assuming things that may not be true of all people, and then using that to draw very broad strokes which may have a steep rate of false predictions.

Forty hours a week is an theoretical standard; it says little about the actual hours put in by programmers. Urban lore suggests the accurate number is higher, sometimes much higher.

The free time a programmer isn't guaranteed to be available in large chunks for hacking. There are a number of things that can take up that time; some of them are bogus, but some are quite reasonable. Enough of that time gets chewed up, the programmer really doesn't have the kind of time they need to focus on deep, substantial projects. Some do find the time, but there are more factors involved than simply motivation.

As for primary and secondary school years, this too depends on a number of factors, not all of them matters of personal motivation and ability.

Assessment is hard enough when you don't have preconceived notions of the molds other people fit into; if you start assessing people already cherry-picking assumptions about them based on what societal fashion suggests is "normal," then your ability to fairly assess them is already screwed. You're not trying to fairly assess them for them; you're doing it for you, because doing it fairly is your best shot at not screwing up.