Part of it's genetics, part of it's diet, part of it's physical labor, and part of it's drugs and alcohol usage. It varies from person to person. Just like with dietary practices too much or too little physical labor can also have an effect on the body, and the same is true with drug usage and alcohol abuse. Some drugs don't age you and others do. Ibuprofen. SSRI's and vitamins won't age you, but a hardcore cocaine or meth addiction over time will. as will extreme alcohol usage.