I have been scouring my book of costume, and did think that I had found something at least kilt like.

There are Egyptian kilts of 4500BC, which do seem to have pleats, and flaps, but that was rather a long time back.

There is no further mention of kilts for several thousand years.

There is the waffenrock, German, 1525, which is a quilted gold brocade item, with shaped pleats basted in in two lines of thread, and two straight bits at the sides, forming just over a semicircle when laid out. Very kiltlike, but alas, the pleats were worn at the front.

There is a quote which mentions the cloth worn by the Scots, which is from Chamberlayne 'The present state of England' 38th edition 1755, saying basically that the English wool was so good in the time of Phillip the Good Duke of Burgundy that all the Scots wore it, from the highest to the lowest, and it brought in so much gold that the Duke established the miitary Order of the Golden Fleece in 1429 when he married Isabel of Portugal. The Staple of English wool was kept in Burgundy - doesn't say why. Perhaps it was not all processed 'at home' but sent out for spinning and weaving in the local fashion whereever it was wanted.

The Duke of Burgundy is depicted in a natty doublet which looks rather like pleats attached to a yoke and set of sleeves - with the shoulders padded and the sleeve tops gathered like something out of Dynasty. It is proper kilt length. The style of the times is for cartridge pleats.

I will need time to study the whole two volumes, but I suspect that kilts and Britain other than England are not going to get much mention.