Brain scans wouldn’t work because our grey matter keeps growing until we are in our 20s

The media furore over dental checks to establish the ages of child migrants arriving from Calais has raised the question of how we define – and prove – adulthood. Dentists have said the checks would likely be inaccurate, not to mention unethical. Brain imaging wouldn’t be much use either, as recent research has shown the brain continues developing right up until the mid-20s and beyond.

Growth of grey matter is very rapid from around the age of 12, but peaks a few years later. What follows in later adolescence is a pruning and sculpting of the many connections that have sprouted during puberty. It could be argued that experiences in this period are as important as earlier ones, and in some ways more significant, as they affect the brain’s frontal lobe which deals with the development of character and morality.

Insurance companies seem to have realised this, as car insurance premiums change depending on your age right into your 20s. And since 2013, child psychologists have worked with under 25s, not just under 18s. It’s just a shame that this is not currently reflected by our asylum policy.

Dr Daniel Glaser is director of Science Gallery at King’s College London