From the October 2009 issue

How did Olympus Mons get to be so tall? Is it because the gravity on Mars is weaker than that on Earth?

Mike Watson, Edmonton, Alberta
By | Published: October 26, 2009 | Last updated on May 18, 2023
December 2009 Mars' Olympus Mons
Mars’ Olympus Mons, the tallest known mountain in the solar system, is 86,610 feet (26,400 meters) high. It easily dwarfs Mount Everest, Earth’s highest mountain on land, both in height and in width.
Astronomy: Roen Kelly

Ultimately, volcanic mountains on Mars are higher because they have more time to grow.