The fundamental problem with this approach is the difficulty in quantifying many of these things. How do you objectively determine maturity, ability to react properly under various intense situation, intelligence, even certain physical elements are difficult to quantify. The arbitrary limits at certain ages are meant there to filter out the 90%+ that is known to fail these tests in general, at the detriment of the remaining percentage, knowing that the benefit of allowing the remaining percentage is insignificant compared to the risks and costs. On a case by case individual basis you can make moral arguments for sure, and the justice system and regular life tend to accept these up to a certain point. But some hard red line is required. As a final thought, why not let 12 years olds consent as well? In my view that is where the authors logic tends towards.
There are some places, (like coasters? ), for which there is minimum height or weight of the person. And no nonsense about age or whatever other irrelevant attribute.
But they are very rare. Sadly.