Our nervous system is a malleable vehicle. Physiology overall is sensitive to genetic abnormalities. DNA base changes can have devastating consequences such as multiple sclerosis or other debilitating pathologies. Outside of the significant but minority cases which inhibit this severely, the body is overall a malleable structure. This is determined by the work you do or how your nervous system is used. A simple example: if you sit excessively you can develop a hunched over posture. This is a change in the magnitude of nervous energy to certain muscle groups in your musculoskeletal system. Learning a language or how to code causes many neuronal connections to be made in the correlated brain region. Both of these phenomena make up what's called neuroplasticity.
Learning new skills affects different lobes in the brain, in that it creates neuronal connections. Much of this is connected to the nervous system and how it is expressed. I.E. you learn the proper technique to play tennis, the proper motor groups connect with muscles. Training something like a backhand also affects the magnitude of energy which is produced by mechanical work in muscle sarcomeres. These nerve impulses stem from the motor cortex and that section of the brain is strengthened when it is used. This also applies to the auditory and other sections of the brain. Neuroplasticity, and the rate which you can rapidly affect these connections, seem to work on a negative curve correlated to age.
It is commonly cited that many major personality factors are set by age three. The brain seems to stop developing in size around the age of 25. Neuroplasticity can and does continue until you die. Your brain adjusts daily to the tasks and patterns which you expose it to. Baseline neuroplasticity is affected by many factors. These include trauma and anything a young or old brain is exposed to. If the brain is exposed to things which require critical thinking/problem solving, those parts of the brain will be trained and developed.
How to Influence Neuroplasticity
There are many methods that people use to influence neuroplasticity. These include meditation, diet, and exercise to name a few.
1) Diet seems to be largely a negative or positive variable. The better and more optimized it is, the better your nervous system functions and will function long-term (barring potential genetic exceptions). There is evidence that the ketogenic diet has a variety of positive effects on brain health. Ketogenic benefits in mind, I recommend using it sparingly. Remember plant fats exist and test and see what foods your body reacts best to (whether it is a fat-based or carbohydrate-based, or whether you do better with fewer animal products). The bacterial composition of your gut also influences your chemical messenger composition. This is also affected by what you eat, so optimizing your diet impacts your mental health in multiple ways.
2) Meditation is another story. It works to regulate neurochemicals, and this is what impacts neuroplasticity (1). Studies have shown that meditation upregulates inhibitory, relaxation neurochemicals which such as GABA (1). This also inversely applies to stress hormones (such as cortisol) and the central nervous system response. If you meditate in a negative set of circumstance or excessively, it can serve to deaden the nervous response. In this way, meditation can act like a drug. That in mind, you can use this technique like a governing tool. If you have issues with excessive stress, you can use a speedometer as an analogy. Moving into the red is damaging and uses excess gas, but excess will slow your cognition. Unlike a gas pedal, we don't really have control over this in reality. Life can throw many stressors at you at once, forcing you to redline. This is where meditation can serve to bring the tachometer more to the center. Obviously, excess practice may cause you to slow cognitively and be more 'spaced out.' This is likely due to a deficiency of stress hormones relative to inhibitory hormones (like serotonin).
3) Exercise also influences neuroplasticity in both parts of the nervous system (central and peripheral). This is due to BDNF and other factors which are released when you train. There is also data which shows exercise can enhance performing complex cognitive tasks (if done following exercise) and creativity.
(1) Divya Krishnakumar, Michael R Hamblin, and Shanmugamurthy Lakshmanan. Meditation and Yoga can Modulate Brain Mechanisms that Affect Behavior and Anxiety. Anc Sci. Published in final edited form as: Anc Sci. 2015 Apr; 2(1): 13–19. doi: 10.14259/as.v2i1.171