Many factors - too many to list, that is your genes (important), stress, exposure to sunlight, smoking, pollution, exercsie and food.

In general, take lots of food that in anti-oxidants. Lots of good Vit-C will be one of your main defence. We age quicker because of the free radical exposure (caused by pollution, stress, natural by product of being alive). Anti-oxidants protects use from these damages.

So the way to counter it is to slow it down by eating lots of anti-oxidant rich foods (things like blueberries, avocadoes, Lots of Vit-C), and to prevent/minimize effects of free radical damange by cutting down stress, smoking, excessive sunlight in the noon, not over-exercisting. You can try facial exercises and massage with coconut oil. THere are lots of things you can do where you can research online.

Honesty, I doubt those collagen drinks/supplements will do any good. They are very expensive. Collagen is just a protein. When you ingest proteins, they get broken down into amino acids and get rebuild again into the suitable structure for use.

INstead of taking collagen supplments, I think it would be better if you stimulate your body to produce collagen instead (we lose this ability / collagen as we age). Something that would definitely help is VItamin C and MSM ie methylsulfonylmethane (organic sulfur). Vitamin C stimulates collagen production and MSM (sulfur) is necessary for building collagen. Sulfur is part of the materials in your cartillage, tendons, ligatments, collagen. VIt C+ MSM works together

MSM is not widely heard but is very useful. You can't find it here (at least cheap). The Vit-C + MSM combo (in high doses - ie 6000mg or more for both) is used as an alternative way for cancer treatment. For Vit-C, most are useless. You can get eithe those made in powder form from berries or the latest tech - lyposomal Vit-C.

You can see many beauty conscious girls on the internet which claimed that taking MSM powder/pills have helped tremendously in their skin (making them healthy , and even fairer). This is a long post - I believe you can learn a lot here - just build on here and do you reseach according to your needs.