I'm a 15 year old girl and the skin on my elbows and antecubital space is darker and more rigid. Could you help me?

Likely Eczema. Eczema is a chronic inflammatory skin condition that often occurs on the wrists and antecubital region of arms leading to discoloration, scaling, redness, and itching. You might have a family history of this condition as it tends to be passed on genetically. Eczema can be mild, moderate or severe and is treated with topical steroid creams and daily moisturization. See doctor for more details.