No. 'Fantastic Beasts' is a series mainly about magical creatures in the wizarding world, with themes of adventure, magic, and friendship. It has no relation to erotic fiction at all.
The story of Fantastic Beasts is rooted in the magical universe of Harry Potter. It expands on the wizarding world and introduces new characters and creatures. Rowling's imagination is the foundation for this enchanting narrative.
The characters in the Fantastic Beasts novels aren't younger. Their ages are appropriately set to drive the story forward and create the intended narrative impact.