I took the Leaving Certificate ( age 16) and five subjects at Matriculation - A level equivalent - (age 17) in Australia.
I took a post-graduate examination within a month of my return to the UK. I passed that. I was 18 years and one month old, not quite the youngest ever candidate because someone else had passed it at 18 years and one week.
I got A's pretty much on everything...Organic chemistry gave me a run for my money as well as human A&P due to the sheer volume of rote memorization required for it but they were the 2 proudest and only C's I ever earned...neither class had more than 10 people pass and neither had an A.