Most Helpful Guy
It's because of the melanin in their skin. Melanin is the pigment which gives your skin, hair and iris its color. One of it's main primary duty is to repel the skin from the intense UV rays that comes from the Sun, so it basically acts as a natural sunblock/sunscreen.
Black people (along with anyone with colored skin like Asians, Indians, some Latinos and etc) has a larger density of melanin in their skin, which benefits them greatly since it slows down their chances of photoaging, which is why they age so gracefully on average.
Most Helpful Girl
I always thought it has something to do with moisturising skin. Like white people naturally have oilier skin and hair and don't put anything on their face, black people naturally have drier skin and hair and tend to moisturise.
Moisturising skin helps keep elasticity in it, which helps you have less wrinkles and less stretch marks. That's why some fat people don't have stretch marks while some slim people do... it's just about elasticity in their skin. But i think it's similar for wrinkles.