Adolescence no longer ends when people hit 18, according to updated guidelines being given to UK child psychologists.
The new directive is designed to extend the age range that child psychologists can work with from 18 years old up to 25.
It is hoped the initiative will stop children being "rushed" through their childhood and feeling pressured to achieve key milestones quickly, reports the BBC.
There are now three stages of adolescence, according to the BBC report: early adolescence that ranges from 12 to 14 years; middle adolescence, from 15 to 17 years; and 18 and over is classed as late adolescence.
It has been introduced because research now suggests the brain continues developing through and past teenage years, well into a person's mid-twenties and thirties.
The new guidance is also to make ensure that over-18s don't miss out on opportunities, or are forgotten about, in terms of health and education.