When it comes to the adolescent and early adult stages of human development, age ain’t nothin’ but a number. We have physical, emotional and intellectual development to consider when we assign ourselves an age independent of the amount of days we’ve spent on earth.

My “man strength” didn’t come until age 19. In fact, during my senior year of high school, my best bolt on the baseball field produced nothing but a warning track fly ball. Two years later, that same ball whistled beyond the chain link fence at Moorpark College in Southern California. While females usually achieve their full physical height by around 16-17, males may continue to develop in both height and weight until 18-19, even into the early twenties for some. Physical development generally happens in the same order for most humans, but the timing can vary widely.

Critically though, this physical development is not necessarily linked to emotional or cognitive progression. I asked my think partner, Stephanie, to do some research on the science behind this. This is what she produced:

While our brains do not grow the same way our muscles do, significant physical changes occur in the brain itself. White matter increases, gray matter decreases, and there is an increase in myelination. In fact, during this period of development, approximately 40% of the synapses in your brain will be eliminated for a more efficient, streamlined organ. These changes have significant impact on emotional and impulse control, long term decision making, evaluation of risks, and adaptation to stress.

These changes occur throughout the ages of around 10-25, and it is difficult to peg where a particular individual is on the spectrum. Mentally, I was sharp and prepared to handle adversity at 14 or 15 years old. My 15 year old son, Chase, may be following a similar developmental path. He’s equipped to navigate failure today, but he’s still patiently waiting for his full physical development to occur. This makes sense – while we can adequately describe the physical processes occurring, both in the body and brain, our actual development is shaped well beyond simply the mechanisms at work. From Harvard Health:

…human brain development does not unfold automatically and uniformly. There is much individual variation that reflects experience as well as genetic programming. The problems of teenagers are not all in their brains but have many causes, social and individual, genetic and environmental. At present and probably for a long time, researchers will be getting better information on the mental and emotional development of adolescents from interviews, observations, and behavioral tests than from brain scans.

Because of the rapid physical and emotional growth of a toddler, it can be easy to look for milestones. In the late teenage years, the effects of our physiology are no less dramatic but more complicated to pin down precisely. It’s utter absurdity to suggest, “he’s 19 and therefore he is experiencing x, y and z inside his body and his mind.” From Jeffrey Arnett (pdf link), psychology professor:

These changes over the past half century have altered the nature of development in the late teens and early twenties for young people in industrialized societies. Because marriage and parenthood are delayed until the midtwenties or late twenties for most people, it is no longer normative for the late teens and early twenties to be a time of entering and settling into long-term adult roles. On the contrary, these years are more typically a period of frequent change and exploration

Sure, we can acquire a baseline armed with the data point of actual age. However, all 19 year olds are not created equal. There is a wide range of maturity, physically and mentally, for every young adult. We’ve all encountered men and women several years wiser or less mature than their peers, and it’s critical to consider this when analyzing the development of friends, colleagues and young ones. Staying open minded and nimble in our assessments is thematic to this blog, and we will not be boxed in by birthdate.

Strong mind,

Kap