My thoughts for what they are worth, the Irish as a Celtic race have peopled Scotland in ages past and the Scots from Ireland landed in Scotland at Dalriada present day Argyle, the flow of peoples back and forth to Ulster and Scotland throughout the centuries eventually formed Ulster Scots with clan associations and tartans to this day, however, to my knowledge I don't know of an Irish Regiment associated with the British Army that wear a kilt except the Irish Guards pipers, who wear a saffron kilt and Irish caubeen(hat).
During the Irish "troubles" wars of independance some Irish politicians wore kilts.
Getting back to the photo of this young man, it seems to be an assortment of puzzles, the glengarry is correct and the hackle in it, the spats and the hose have the dicing of the Argyle and Sutherland Highlanders, the doublet looks like a piper's though the sporran is not A&SH, The cantle badge is another puzzle and I cant find any thing like it on Scottish Regiments,
It has the Victorian crown above what appears to be a foot regiment badge - google any foot regiment from 24th foot 29 35 46 48 53 61 64 69 80 83 94 96 97 and 98th foot.
Other options I have looked at include Queen Victoria's School Dunblane and although there is some resemblance to their badge I don't think it is. Ampleforth College didn't match either.
Tyneside Scottish, London Scottish didn't match and Liverpool Scottish 8th Scottish Volunteer Battalion was an option but the cantle badge was different.
So your young man appears no nearer to identification. Reference the gloves, pipers will sometimes wear gloves with the tips removed to expose the first joint of the fingers when it is very cold, Brigade of Guards wear gloves on public duties in winter and line regiments wear gloves in parade dress, Ive even seen Gurkha regiments wear gloves on London Public duties.
Though I agree with Barryd that he is a soldier from a Scottish military organisation, Cadet, School or Territorial.?
Apologies for wittering on but your man is "getting to me" now and I will continue looking.
As you know there are people on here who can give you chapter and verse just on a name, does he have a name?
James