Mum2422 mentioned in her OP that her dcs were "youngest in the classes" at the moment. That would suggest August or July birthdays or possibly June.
That would put them solidly in the "older" end of their respective years in Scotland, but by no means the oldest, especially once you factor in deferrals.
Ds has a September birthday: that made him technically slap bang in the middle of the cohort in Scotland, but in practice, because of deferrals, he was actually at the young end of the year.
It also meant that even though he did S6, he was still 17 when he started Uni
(turned 18 when lectures started, having not been able to drink officially during Freshers Week).
If he'd been in England, he'd have been one of the oldest in the year below.
To illustrate the range in Scotland, one of his friends in his class (who had deferred), turned 18 in the December of S6. Another friend in his class (who was the cleverest in the year), who hadn't deferred, only turned 17 in the February of S6 (so ended up being 17 for almost his entire 1st year of Uni
).