Here's President Donald Trump on the day of his inauguration in January 2017. He was 70 when he took office, the oldest in US history.
British Prime Minister Theresa May came to power in 2016 during a chaotic political time while Britain decided whether or not to remain part of the European Union.
Canadian Prime Minister Justin Trudeau became leader in 2015, after a surprise victory ousting a government that had been in power for the previous 9 years. He was 43.
Source: Washington Post
India's Prime Minister Narendra Modi was elected in a historic landslide victory in 2014. He was 63.
Source: The Guardian
Xi Jinping became China's president in 2013, after being elected general secretary of the Communist Party in 2012. He was 59.
Other than some grey hairs, China's most powerful leader since Mao Zedong doesn't look too different.
Source: BBC News
Venezuelan President Nicolás Maduro assumed power at age 50 in 2013 after the death of former President Hugo Chavez.
Source: AP
In 2019 he's looking a little weathered, which makes sense considering the country's weak economy and a continuing struggle over who the legitimate Venezuelan president should be.
Source: Vox
North Korean supreme leader Kim Jong Un came to power as one of the youngest world leaders in 2011 after his father, Kim Jong-Il, died. At age 30, he inherited a nuclear arsenal and a bevy of human rights abuses.
Source: Business Insider
Here he is meeting with Trump in the Demilitarized Zone between the two Koreas in June 2019. A trip to Beijing in 2018 was his first known time outside of North Korea since becoming leader.
Source: Business Insider
German Chancellor Angela Merkel, the country's first elected female leader, came to power in 2006 at age 51.
Source: BBC News
Here she is in 2019 after 13 years as Germany's leader. She's said her current term, her fourth, will be her last.
Source: NPR
Japan's Prime Minister Shinzo Abe was elected in 2006, but stepped down after a year in office, citing health issues.
Source: BBC News
He was re-elected as prime minister in 2012, and in 2019 he's on track to become Japan's longest-serving Prime Minister. Abe is now 64.
Source: The Guardian
Recep Tayyip Erdogan was elected as the president of Turkey in 2014, after also serving as prime minister for 11 years. This is him in 2002.
Source: BBC News
At age 65 in 2019, Erdogan is looking older after a particularly stressful year when his party twice lost the mayoral race for Istanbul. He's previously said that when the city was lost, the country would be, too.
Source: Al-Monitor
Russian leader Vladimir Putin became prime minister in 1999 after working as a spy and security chief. In 2000 he went on to become president when Boris Yeltsin resigned. He was 47.
Sources: CNN, The New York Times
Israel's Prime Minister Benjamin Netanyahu was elected in 1996 and again in 2009 after a 10-year gap.
Here he is at age 69 in 2019. In April, it looked like he had won a fifth term as prime minister, but after failing to produce a coalition government, Israel will decide who its leader will be in September.
In 1981, Ayatollah Ali Khamenei became Iran's president at age 42. He served in that role until 1989, when he became Iran's supreme leader, which he still is today.
Source: CNN
Equatorial Guinea's president Teodoro Obiang Nguema has been in power since a military coup in 1979. He is the world's longest currently serving world leader.
Source: Nation