We have around 20 student members aged 14 to 16 and they all, with few exceptions, think in metres.
Initially we teach them to estimate ranges with the mark 1 eyeball. That's hard enough without having to get them to adapt to yards.
FT could have a 50m limit quite easily.
Once you have newbies ranging in metres and kill zones in millimetres and understanding what a mildot is, it all clicks - no pun - into place.