While the law might declare people as adults when they turn 18 - scientists have discovered that thirty is the real age our brains reach adulthood, according to the BBC.
What's more? Scientists who study the brain and nervous system say the age at which you become an adult is different for everyone.
Research suggests people aged 18 are still going through changes in the brain which can affect behaviour and make them more likely to develop mental health disorders.
Professor Peter Jones, from Cambridge University, said: "What we're really saying is that to have a definition of when you move from childhood to adulthood looks increasingly absurd.
"It's a much more nuanced transition that takes place over three decades."
He added: "I guess systems like the education system, the health system and the legal system make it convenient for themselves by having definitions."