Romero had already climbed five peaks, including Mount Kilimanjaro in Africa, but has yet to climb the highest peak in Antarctica.
The previous youngest person to summit Everest was 16-year-old Temba Tsheri Sherpa of Nepal.
Accompanied by family
Romero was accompanied by a team including his father Paul, a critical-care paramedic, and Sherpa guides.
He told Reuters his aim was to pick a small piece of rock from the top of the world as a memento and wear it on a necklace.
His next mission is to climb the highest mountains in all 50 states in the US.
More than 4,000 climbers have reached the top of Everest since it was first climbed by Sir Edmund Hillary, a New Zealander, and Tenzing Norgay Sherpa, a Nepalese, in 1953.
On the same day as Romero, Apa Sherpa, a Nepali mountaineer, broke his own record and climbed Everest for the 20th time, Ang Tshering Sherpa, chief of the Asian Trekking Agency, said.
Apa, 50, who lives in the US, reached the summit on Saturday along the Southeast Ridge route.
He carried a banner all the way to the summit to raise awareness of the environmental impact of climate change on the Himalayas.