It is hard to say. There are some reason that maybe why old people wear sunglasses. First of all, maybe they need sunglasses to protect their eyes. You know, cataract often occur to older people. And wearing sunglasses can protect the eyes from sunlight, thus to prevent cataract Besides, most of older people suffered from presbyopia. wearing sunglasses with prescription lenses can help them see better. What's more, wear sunglasses can make them look better since sunglasses can cover their eye wrinkles. And sunglasses themselves are nice accessories.