Sexual desires may begin before children are 18, but it doesn’t mean that pornography is necessary. Many children’s desires simply take the form of curiosity, where they are exploring their bodies for the first time and learning about who they are. Many sexually active people, for example, remain sexually active without watching pornography. Evolutionarily, there is a desire to reproduce, not to watch videos made of other people reproducing. Therefore, the right for humans to eventually choose to reproduce and control their own bodies is a guaranteed right, but the right to watch videos of it that mislead youth into false sexual fantasies and force them down a rabbit hole of increasingly dark sexual desires is not a guaranteed right for anyone.
For a minor, puberty is still a stage in development. Minors might feel a sexual desire, but that does not mean they should act on it at such a young age. Going through puberty does not mean you have properly developed adult abilities to balance sexual desires and other aspects of life. This could explain why minors are likely to become addicted to porn at such an early age when they are still at the crossroads of being sexually active and being able to make mature decisions.