Age verification... well if you want to call it that... i would not.
Its simple:
All they do is ask about your birth date. Thats it, you can fill in what you want there, thats really no real verification. No passport or something like that is needed... Which is a yearly topic of our child protection community and law, but they dont do much besides talking.
Well the stronger "age verification" is the essential payment method though... you cant open up a paypal account without being 18. You cant have a creditcard without being 18. Same goes for a full bank account. Those things have a really good verification of course and without a valid payment method, no working steam/epic/gog account. But most parents dont care obviously and just open up a account for their kids so they can do what they want and so on, they deal with the problems when its already too late...
Besides, i dont think underage people have much intereset in a Visual Novel... because... well they need to read and the whole game is basically a book, not that popular around teenagers these days.
But
dluser is not wrong... we went way to deep in those things and they dont really matter for the game anymore...