I am living in Scandinavia and my DH has worked with underaged minors (14 to 18) for the past 4 years. This country took in the highest number of refugees in Europe per capita in 2016.
My DH and his colleagues say around 50-60 per cent lie about their age. It is not true that the 'minors' are age tested in this country. But there have been lots of calls to do it. It has been said that dental and bone density scans can give a reading to within 2 years. My DH and his colleagues say that if you had a cut off of 20 - for a scan, giving a 2 year grace, you could rule out the over 20 year olds for a start off. One of the refugees was actually called Papa by the others because he was supposedly married with children but was at the local high school. I have mistaken minors for his work colleagues several times. My DH said that looks aside one of the tell tale signs was that the older ones were generally secretive and kept a low profile. They would talk about the journey but not about the life from where they fled. The genuine under aged minors at some point behave like ordinary teenagers - had petty squabbles with each other, behaved petulantly and said 'its not fair' they were very open about their lives and eager to get in touch with family. The older ones did nothing to draw attention to themselves.
There is enormous benefit to being classified as a minor. Housed in a HVB home, free medical care, education, legal service. Local activities - football, basketball, badminton all free. They get a laptop for school work and assigned as mentor outside of the home. Once over 18 they are given flats and furniture allowance and access to on call help until 21. There was also no question of them being denied the right to stay until 18.
Over 18s (adults) where refugee status is being determined are sent to a converted barracks (now closed due to more families and less lone young men) and although free to come and go there were not the benefits or leg up from being classed as a minor.
Most definitely there were older men at the one local school.