For someone to help you, you need to tell us what kind of soil you used, & how much and how often you're watering. It could also be ph related. That's one reason why we need to know about the soil. Something is definitely wrong for a large fan leaf to go yellow when the plant is that young. If it were outdoors, I'd tell you to look for bites on the leaves, as this is often caused outdoors by the Six Spotted Leafhopper, also known as the Aster Leafhopper, spreading a phytoplasma disease to plants called Aster Yellows, but I seriously doubt that's what you're experiencing, and good thing, as there's no cure for it.