He far exceeded that, becoming the top Army commander a few years ago and is now set to be installed as the next prime minister.
The National Legislative Assembly yesterday voted for him to become the 29th prime minister of the country, pending royal endorsement.
At age 15, Prayuth disclosed his passion to be a soldier. He told the now-defunct Chaiyapruk student-oriented magazine in 1969 that he was inspired by his father, who was an Army colonel.
As an outstanding student, he was interviewed by the magazine for its "Rian Dee" (Good Student) column.
Then secondary school student, Prayuth was described in the article as being mature beyond his years, and unlike most of his classmates spent most of his time reading and studying rather than playing outdoors.
The magazine reported that Prayuth had not got less than 80 per cent on an exam since primary school. He liked maths, English and science, saying his recipe for academic success was his love of studying.
The article's author said Prayuth had a bright future, and that the chance of him going off the rails was "very slim".
Prayuth went on to achieve his childhood dream, joining the Armed Forces Academies Preparatory School. As a member of Class 12, he began nurturing his ties with Class 10 member Anupong Paochinda, who later became Army chief.
This relationship proved a significant factor in Prayuth's rise through the ranks. The two watched each other's back when they served in the elite 21st Infantry Regiment of the Queen's Guards in Chon Buri.
Prayuth was born in 1954 in Nakhon Ratchasima to Colonel Praput and Kempetch Chan-ocha. He has four siblings and one of his brothers, Lt-General Preecha Chan-ocha, is the Third Army Region chief.
He attended Nuannoradit School before joining the pre-cadet school and then the Chulachomklao Royal Military Academy as a member of Class 23. He became Army commander-in-chief in 2010.
The PM-elect is known for his fiery temperament. On May 22, the day of the coup, he declared that he decided to seize power after arguing politicians failed to end their dispute during a meeting he had brokered.
Former sociology teacher, Thani Kumchana, 74, who taught Prayuth as a boy at Wat Nuannoradit School in Bangkok, said she was very happy to hear that her former student would become the 29th PM. She described him as a quiet student who worked hard. He was also very honest.
She said he loved school and had always supported and helped the school in any way he could since starting his career in the military.
School director Prasert Poodpong said, according to former classmates, Prayuth was rather quiet but a great student who loved to read and was very determined. He loved playing football and loved his school. He donated Bt200,000 to the school earlier this month. His classmates said Prayuth was also the best looking boy in the class.