It has been a summer of surprises for observers of Saudi Arabia.

On 5 June, Riyadh, supported by other GCC and Arab states, announced it had broken off relations with Qatar and halted land, air and sea traffic with the country.

And then came the news that Deputy Crown Prince Mohammed bin Salman al-Saud had replaced his cousin Prince Mohammed bin Nayef as heir to the Saudi throne.

This overshadowed oil prices the same day falling to their lowest level since Saudi Arabia forged a production restraint deal involving Opec and leading non-Opec oil exporters in December. And it deflected attention from the recapture, completed on 9 July, of Mosul from Islamic State in Iraq and Syria.

The fascination with the new crown prince is due to his age. He is 31 and was largely unknown before his father became king in January 2015.

The plan he has championed to transform the Saudi economy by 2030 and Riyadh’s intervention in Yemen, which he approved as defence minister in March 2015, are both contentious. Prince Mohammed was under 30 when these policies were adopted.

But there is a precedent. Prince Mohammed’s grandfather Abdulaziz al-Saud was 27 when he recaptured Riyadh for the Al-Saud dynasty and became emir of the Najd. By the time he was 31, Abdulaziz had expelled Ottoman forces from central Arabia. He seized Arabia’s eastern region before he was 40. Jeddah, Mecca and Medina were taken in 1925. Abdulaziz became Saudi Arabia’s first king seven years later.

King Salman himself tasted power early. His father made him deputy governor of the Riyadh province when he was just 19. He became its governor before he was 30.

Arabia has only recently been a place ruled by old men. Prince Mohammed’s rise echoes an earlier tradition, where youth and ambition trumped experience.

But it would have been impossible without the approval of King Salman, now in his 82nd year. He and leading Saudi princes have decided that the last thing the country needs is another period in which possible successors feud and ministries drift as an ageing king’s powers fade. This is what happened for 10 years after King Fahd’s stroke in 1995 and for half a decade before King Abdullah’s death.

King Salman has used the legitimacy he enjoys and the right Saudi Arabia’s laws allow him to name as his heir a capable son he loves and trusts. It would have been more surprising if he had not.