Nobody is banning the youth from accessing wikipedia or a library or minecraft.
Wikipedia has pornographic images and videos in it (certainly in its media archive, Wikimedia Commons, and some of them are embedded in articles).
Library: ??? Are we still talking about the Internet?
But also, if the parents decide that it’s part of growing up they can just give their kids access to porn.
Yes. Giving kids access to the open Internet is giving them access to a repository of nearly all human knowledge and endeavors, including (but not limited to) porn. If parents believe their child isn't yet developmentally ready to be exposed to all human knowledge and endeavors, they shouldn't be giving that child (unsupervised) access to a worldwide information system whose entire purpose is to provide access to exactly that.