At 20, lines under the eyes are not necessarily a sign of aging—especially if you’ve had them for as long as you can remember. Genetics and your natural facial anatomy are often the biggest factors. Some people naturally have a more visible tear-trough or a slight crease where the lower eyelid meets the cheek. The thickness of the skin, the shape of the underlying bone, the amount of fat in the area, and how the light hits the face can all make these lines more noticeable. If they’ve always been there, that makes a genetic or anatomical cause much more likely than premature aging. Sleep can definitely make the area look worse temporarily. When you’re tired, the skin may look a little duller or the under-eye area may appear darker or more sunken, but poor sleep alone would not usually create a permanent line that has been present for years. Allergies can also contribute to under-eye changes, but since you don't have allergies, that is less likely to be the main factor. For improvement, I would start with the basics: consistent sleep, daily sunscreen, a gentle moisturizer, and avoiding rubbing or pulling on the delicate under-eye skin. A low-strength retinoid may help with very fine lines and skin texture over time, but the under-eye area is sensitive, so it needs to be used cautiously and not too close to the eyes. If the lines are primarily due to your anatomy or tear-trough shape, skincare may only make a modest difference. Treatments such as laser or other skin-resurfacing procedures can help when the issue is mainly skin texture. Filler is sometimes used for tear-trough hollowing, but at age 20 I would be very conservative about considering filler because the under-eye area is anatomically delicate and filler can have complications. Most importantly, having these lines at 20 does not mean that you are aging prematurely. If they've been there your whole life, they are very likely just part of your natural facial anatomy.