In truth, Ling Han, too, could try breaking through to the Spiritual Infant Tier, but he chose to delay it.
In his last life, he was only concerned with pursuing advancement through cultivation levels, but in this life, he naturally would not be so rash. Instead, he wanted to perfect his cultivation on every cultivation level before he chose to begin breaking through.
Anyways, he was still young, not even twenty years old yet, so there was no need for him to rush.
He wanted to form thirty flashes of Sword Qi and develop the Indestructible Heaven Scroll until the Diamond Tier before breaking through to the Spiritual Infant Tier. This way, when he raised his Spiritual Infant, it would be tempered by his Sword Ray and supported by the Indestructible Heaven Scroll, so it would be indestructible.