(CNN) -- One of Uganda's last remaining kings turned 18 in a boisterous four-day ceremony that ended Sunday and allowed him to take full control of his kingdom in the western part of the country.

King Oyo is among the world's youngest reigning monarchs. He ascended to the throne at age 3 after his father died in 1995.

As a minor, kingdom officials had appointed a board of advisers to help him rule.

The board was disbanded to mark his birthday, which means the teen can now make major kingdom decisions on his own without consulting with his advisers.

"He needs to use this opportunity to help us help ourselves," said Sarah Namara, 25. "He has a lot of work to do especially in ensuring people our age have businesses opportunities."

The high school student -- whose full name is Oyo Nyimba Kabamba Iguru Rukidi IV -- rules over about 2 million people in the largely impoverished Tooro kingdom.

He also oversees a Cabinet that includes a prime minister, board of regents and councilmen.

For his coming of age, his subjects gave him a spear -- a symbol of his role as their protector. His mother, Queen Best Kemigisa, gave him a Mercedes Benz.

Turning 18 is " a huge responsibility," the king said earlier this year. "But I have a lot of support from my mother, my sister and others, so I know I can do it."

Ugandan President Yoweri Museveni, one of his former advisers, also attended the events.

Other birthday festivities included a church service with leaders of various denominations and an address where he pledged to help the youth in his largely uneducated kingdom.

"I hope he keeps his promise because education is the only way we can move forward," said Rodgers Barozi, 20, a receptionist in Fort Portal

The king also urged residents to work hard to attain self-sufficiency using the kingdom's rich agricultural history. The lush region has rich brown soil and is a major source of bananas and other agricultural products.

King Oyo serves as a figurehead for the Batooro people, who make up most of the kingdom. His roles include promoting cultural pride and helping raise funds for issues such as health and education in his kingdom. The teen also helps oversee tax money his kingdom gets from the Ugandan government.

Kingdoms in Africa date to the Egyptian civilization, though their numbers have declined in the past few hundred years. The monarchies are based on ethnicities.

In Uganda, the central government outlawed kingdoms in 1967. The president reinstated four of them in the '90s on the condition that their leaders focus more on culture and less on national politics.

Other African countries, such as Lesotho and Swaziland, also have kings.

Journalist Samson Ntale contributed to this report.