What Causes Wrinkled Skin?

hi m 49 years old 5:5 tall 63 kg but compared to my age or older ladies , i feel my hands specially wrist and fingers look wrinkled ..i do have thyroid prob from past 10 years and taking Thyronorm 100mcg tab daily.why my skin only on hand and feet looks wrinkled..than other similer or older aged onse and than th rest of my body ?