Why does the way of thinking change with age?

With the growth of age, the mentality must change. When I was a child, because my family was poor, compared with others, I was poor in food and clothing, pessimistic and unwilling to join the group. When I grow up, I find that as long as I study hard and get excellent grades, I can make others sit up and take notice. My mentality is to study hard and never admit defeat. After entering the society, I meet different people and hear different voices. My mentality is that the society is very complicated, and I am careful what I say and do, lest I make mistakes.