In humans, youth is characterized by a clearly discernible period of physical and mental development. As our cells multiply, our bodies become bigger and stronger – and as we continue to take in knowledge, our cognitive abilities increase. But as we are well aware, something goes awry in the cell renewal process when we reach the 20-35 year old mark. We begin to lose our ability to respond favorably to stressors, biological homeostasis decreases and we become more prone to diseases. In a nutshell, we begin to age.