These days, a lot of young people treat their twenties as an “extended adolescence.” Where they live at home, hang with their friends, and wait to figure out what they want to do with their lives. There are even cutesy nicknames for the age group, like “twixters” and “kidults.”

But Dr. Meg Jay - a clinical psychologist who wrote the book The Defining Decade – Why Your Twenties Matter – says that’s a mistake. Because when a young person thinks they have another 10 years before they have to make any important decisions, they end up playing a waiting game. And when they hit 30, they’re suddenly pressured to find a partner, choose what city to live in, build a career, and have children, all in a short period of time.

In fact, Dr. Jay believes that a person’s twenties are the most important, defining, and formative decade of adulthood. The time when you’ve got the energy and the ambition to take important steps in your life, your personality, and your career that can impact your entire future. 

For example, the first 10 years of your career can determine how much money you’ll earn for the rest of your working life.

Also, your personality changes more in your twenties than at any other time in life. Because that’s when the human brain has its final growth spurt, and re-wires itself for adulthood. Which means, whatever it is you want to change about yourself, that’s the time to change it.

What’s the most important advice Dr. Jay has for twentysomethings? Expand your circle. After all, if you only hang out with people who are just like you, you won’t discover anything new. And you’ll never know what new ideas, places and people are out there if you only hang out with people in your comfort zone. 

Again – the book is The Defining Decade: Why Your Twenties Matter.