Stickerrocks he must have been put up a year because you do NAT5s in S4 (Secondary year 4) when you are either 16 or 15, but about to turn 16.
They don't cram 2 years of A level into 1 year of Higher.
Highers are a 12 month course (with all the usual school holidays). So the students that have just finished their Nat 5s will be starting their Higher courses now and taking them this time last year. Whereas in England, all our children won't be doing anything until September.
Also the Highers are less deep than the A levels. Typically students take 5 of them, whereas here its only 3. However, the Scottish universities pick up where Highers leave off, so the english students who go to university in Scotland find that they are going over old ground at first. IME, they find the first term at university in Scotland is like year 13 i terms of content, but from January onwards they are doing new stuff. (The English students I knew thought they were going to be a whole year ahead and got a bit of a shock after Christmas).
But Scotland does 4 year honours courses, not 3, so although you go to university behind the English students who've done A levels, your age group in England join a year later and you finish at the same time.
I don't know how the advanced Higher thing works. My fear is it relates to the "narrowing the gap" that the SNP obsesses over, which in practice means holding the more able students back so there results look closer to the less able's results.
The pisa rankings indicate that I may be right. Scotland has gone from having an excellent education system to having one that has suffered through political interference.