Especially blacks and east asians.
Genes, of course, along with our biological clock. Genes determine our fitness, our symmetry, our skin, and physical abilities. The taller and/or fatter you are, the more your appear older than you are (there are exceptions of course). Adults with child like features are pretty small in stature.
And you were asking about Asians. They appear smaller in stature and consequently tend to look younger.
There are a gazillion of other factors at play, like how much you stay out of the sun, if you smoke, if you eat your greens etc. But it all comes down to each person’s genetic make-up
Apart from genetics, which contributes to pretty much everything, Asians (and blacks) look younger for several reasons:
Their skin tone is different from Caucasian people. The amount of melanin in the body plays a crucial role in how you age. Therefore people with more melanin can deal with the sun much better, with less damage. Apart from melanin, collagen also affects skin and ageing. Black people have the most of both melanin and collagen, however white people have the least. This is why many black people look years if not decades younger.
Diet also plays a role. Eat foods that are rich in Zinc and Selenium, and eat the rainbow to get vitamins A, B-Complex, C, D3, and E.
The sun!!! It has the biggest ageing effect on your skin. Sun damage is real and it leads to cancer in such a great percentage. Especially if you’re white. So SPF 50+, broad spectrum!