When the state passes bad laws -- laws that the majority of the populace are surely going to circumvent, or laws that require absolute tyranny to strictly enforce -- the inevitable result is that people come to treat the law itself with disrespect or revulsion. The idea that one should be law-abiding as an ethical rule goes right out the window. The concept of the law is debased.

There are very few things that do more harm to society.

Maybe if the age limit was lower, and maybe if the law was less strict. But the delta between this law and the society its being imposed on is way too big to not cause serious unintended consequences. The younger kids will find ways to achieve many of the same interactions, only totally unregulated, and in doing so will be forced to create distance between themselves and 'adult' society.

It's important to note that this only bans under 16s from having an account. They can still watch youtube videos.