There aren’t any measurable elements of personality that are fixed. Personality changes as you age. I’ve witnessed a reversal in each of the Myers-Briggs markers in the past 15 years (from INTJ to ESFP) — not intentionally, but that’s just the way my life played out. I’ve come to see the truth of the matter like this: every human being has a need for socializing, but it takes effort and is exhausting. The amount of e…
People can get more social skills as they age, regardless of their personality, and it may appear as extraversion, but I don't think of it as a core change. You don't have to enjoy socializing to do it, just like you don't need to love your job to be good at it. Introverts with good social skills simply do the necessary amount of socialization to fulfill their needs the go back into their head once their are done.
But while people mature, get new hobbies, get jobs, become parents, etc... Barring extreme situation, their core personality tends to stay the same, they just transfer. For example, an online game addict may end up getting out a lot more and vice versa, but online or outside, if they are extraverts, they will tend to have a lot of social interactions. It is usually apparent when people lose self control.