Australia had some of that fun
A fair while ago they used wrist size to determine age for a group of Indonesians caught fishing illegally in Australian waters. The adults were subject to criminal prosecution and locked up — the minors repatriated as required by Australian and international laws/conventions..
Of course wrist sizes vary a over populations without even taking ethnic variation into account so inevitably some very young boys were also banged up much to the embarrassment of, and cost to the authorities.
In that part of the world (SE Asia) there are some very small people (think adult woman around the size of a 9 year old North European girl) but there are also some fairly robust individuals (think US footballer) so using a single metric based on averages is fraught with danger. Epiphyseal plate closure might be a better metric of age but still not particularly useful as such (it's linked to puberty so highly variable.)
If the population, the civil service, the Home Office and parliamentarians could get through their armour plated skulls that there are no simple solutions to difficult and complicated problems† then some of world's problems might be constructively addressed.
† Probably was on the first tablet of the 10 commandments with the surviving 10 intended as talking points.