Dogs live 12 to 15 years, and the theory says that we can compare the Dog age with human age, multiplying the dog age * 7.
Usually all animals get the maduration of his bodies in a certain time, and they live Maduration Age * 7. That means, if a dog develops his body in 2 years, then he will live 2 * 7 = 14 years approx. Humans develop our bodies in 20 years, that means that we should live 140 years, but we don't live that amount of time.
About vitamin c, I read that humans were able to build Vit C long time ago. But now, we cannot. But we can build Vit D with the aid of the Sun.
I also read somewhere that insulin or sugar, and Vit C are very similar and when we take too much sugar we are destroying the Vit C we store in our bodies and we're destroying the collagen of the body and the arteries and veins loss a lot of elasticity due to the lost of the collagen.
Sharks, in example cannot develop cancer. The reason is cancer and regeneration potential are opposite. I mean, when we have less regeration potential we can have more cancer and viceversa. The sharks are developing teeth again and again. Humans cannot.
"A knot cannot be undone, without knowing the way it was made" Aristotle