Age is a hard characteristic to set developmental attributes to because the computational power of the brain is relevant to how the individual was raised along with their genetics. There are children who seem to be highly introspective and self-aware by the age of 6, and others who don't realize they think the way they think due to external forces until the age of about 16. I'm willing to bet ages 12-14 are probably the average age of personality development. Developmental psychologists may argue temperament as a toddler is more or less a sign of personality while sociological psychologists may say that development of one's own sense of culture is the ultimate milestone of personality.
No i think it's beyond 5 years per inherent nature of where they did be at all stages and how these stages contribute towards their personality is significantly above 5 years
Personality gets developed with the passage of time may be school ,college , influence & subsequent with the career position if lucky enough to have the standing position .
For child certainly his personality development within the range of 5 years play an important part & in this line it is the environment of family including the responsibility of parents to view the study & observation of his child & in this line parents take the necessary action in the light of observation for building the mode of life within the period of 5 years .
It also relies on bio-physiological nuances that facilitate soma and dendrite growth along with unimpinged axonal connections. In other words, regardless of environment, if there are cerebral interruptions then expect behavioral variations which impact what humans describe/label as “personality”. Primacy principled behavior can be changed by unpredicted recency effects that do not have to be environmentally catalyzed; e.g. a cerebral rupture that was not caused by any environmental stress at all; i.e., just genetics. All of which could occur within the first 5 years of life or at any time afterward. The point is that the significance of the first 5 years of life on personality development cannot be assuaged; albeit, a reasonable person understands and expects many possibilities to exist and change throughout one’s life; pursuant to genetics regardless of environment.
Not totally, it's part of that. I think the most effective is the beyond 12 years, however, the behavior of the child may change according to his around circumstances. The child mostly forget the things happened in the first years of his life.
first 6 years of life have great effect on the child behavior later on , in which any insult affecting this libidinal period it will appear in the future as psychological disease such as ( anxiety , conflicts , obsession ,,,, etc )
“We used to think that the brain was fully developed by very early teenager hood and we now realize that the brain doesn't stop developing until mid-20s or even early 30s. There's a lot more information and evidence to suggest that actually brain development in various forms goes on throughout the life span” (Helps, 2013). Consequently, the same is reasonable for scholars to conclude about personality; since all are impacted by environment and frequency of immersion amid particular sets of stimuli coupled with bio-physiological nuances set forth by an individual’s genetics.