Frankly speaking, good skin heavily depends on your genetics.
I know many people who have good genetics that contributes to youthful looking skin.
But, in the long run, maintenance can be the real key. All other authors for this question have addressed nutrition, the role of water, staying away from sunlight etc as agents that can save your skin.
I have another very important agent to add which most people tend to ignore.
Realising the impact of ‘blue light’ (emanating from your laptop & mobile screens) and reducing your exposure. - Many skin care brands are now releasing products that save your skin from visible light, specifically blue light emanating from our digital devices. There is mounting evidence that blue light is leading to photo ageing, wrinkles, hyper-pigmentation on the skin.
Blue light might stimulate the production of free radicals in the skin, which can quicken the pace of skin ageing and cause pigmentation. Blue light aka. longwave UVA has long been associated with triggering excess melanin production in dark-skinned counterparts.
There's also evidence that as blue light penetrates the skin, reactive oxygen species are generated, which leads to DNA damage, thereby causing inflammation and the breakdown of healthy collagen and elastin, as well as hyperpigmentation.
Although the studies are inconclusive on a larger scale, small control groups have proven the effects of Blue light (Both from sun & our digital devices) on different skin types.