There is no generally accepted age, where human aging starts. Some researchers say human aging starts before birth, as even then we have damaged cells, according to some researchers such a definition cannot be made.

For the sake of this conversation and practicality, we will try to establish an age and try to differentiate between growth and age. It’s important to note that distinguishing between growth and aging can be tricky. For example, in certain mouse models, the deletion of growth pathways, such as the mTOR and growth hormone axes, leads to a significant extension of lifespan, suggesting that the lines between growth and aging are blurred. These mice are dwarves and dont have “growth hormone”, yet they also age slower.

In humans, we reach certain milestones, like the closure of growth plates in bones, the full maturation of reproductive organs, and peak physical performance, before we start to see a gradual decline. So, for the purpose of this discussion and anti aging, let’s consider aging as that point where growth stops and declines begin.

When does age-related cognitive decline begin? Timothy A. Salthouse ∗

Age Differences and Changes in Reaction Time: The Baltimore Longitudinal Study of Aging

Over the Hill at 24: Persistent Age-Related Cognitive-Motor Decline in Reaction Times in an Ecologically Valid Video Game Task Begins in Early Adulthood