An interesting thread.

A pal in Castle Douglas area, (yes, lowland!) thinks that kilts, "Dinna' look reet on a skinny bod". He thinks you need to carry some weight to take the kilt well.
Personally the kilts in my mind look the worse hanging dawn way below the knees.
Actually, a slim laddy looks just as bad with an overly Long kilt as does a more thick set type.

So, be you thick (midriff, not head!) or thin, wear it right and it'll look right!

Historically there were many small folk in the highlands, but great strapping fellows were about as well.