The 18-year-old said he wanted to set himself a challenge when he selected a formidable seven subjects to study at A-Level because he found it hard to restrict himself to the usual three choices.
For the last two years, he has been studying biology, chemistry, physics, maths, further maths, Latin and Greek.
Because of the lack of expertise in Greek, Alastair spent hours instructing himself on the subject.
The Royal Belfast Academical Institution pupil is hoping to specialise in chemistry in a four-year undergraduate degree, 3,392 miles away on America’s west coast.
He secured a $64,000 scholarship to attend Stanford University, his first choice, which is known for its expertise in teaching science.
It followed disappointment at the end of last year when Oxford University rejected the promising young student.
“I did try (to apply to) Oxford but I was rejected. They did not give any reasons at all,” the student, who was predicted to get 7A*, told the Belfast Telegraph.
“They just said they didn’t want me.”
But disappointment turned to delight yesterday when he received the best A-Level results seen in Northern Ireland in recent years.
Alastair now hopes to work in science-related research after university.
So what is the secret to the determined teen’s success?
“I did not say I’m going to do three hours a day or anything like that,” he said.
“I just did as much as I needed to until I knew as much as I needed to know.
“It’s absolutely amazing to get into Stanford. I’m so pleased with it all.
“The past few days have been pretty nerve-wracking, but I put the work in.”
A spokesman for Oxford said that, while the university could not comment on individual applications, “admission to Oxford is based purely on aptitude and potential for the chosen course, assessed through a range of measures”.