After becoming the youngest person in the world to climb California's Mount Whitney in a single day, Armstrong, then 7, met Debra and Paul Miller and their son, Hawken, who has Duchenne.
The genetic disorder causes progressive muscle degeneration and weakness and primarily affects boys, with symptoms appearing between ages 3 and 5, according to the Muscular Dystrophy Association. Many children with Duchenne begin using wheelchairs between ages 7 and 12. The disorder also affects the heart and lungs, ultimately proving fatal.
"It was really hard to hear about Duchenne because [the boys affected] are like me – they're the same age as me, but they have really hard problems, especially walking," Armstrong tells PEOPLE. "Boys my age love playing sports and running around, so it's really hard for them. When they work out and walk around, their muscles get smaller and smaller."
After meeting Hawken and learning about the approximately 300,000 other boys around the world who suffer from the incurable disorder, he knew he had to do something.
The ambitious boy set a goal to become the youngest person in the world to climb the Seven Summits – the highest mountain on each continent – to raise money for Duchenne research and spread awareness about the disease.
Armstrong partnered with Cure Duchenne, the foundation started by the Miller family that aims to fund research for a cure. Armstrong has already raised over $15,000 for Duchenne research – and he's set a goal to bring that total to $1 million.
"I'm really glad that I'm helping to cure this disease. My goal is to raise $1 million so that one day the boys with Duchenne will hike with me," he says.
Armstrong has already tackled two of the seven summits, and he'll take on a third in August. In 2012, Tyler climbed Tanzania's Mount Kilimanjaro at just 8 years old. The next year, he became the youngest person to summit Mount Aconcagua in Argentina.
"The boys with Duchenne, they keep me going on every mountain I climb," he says. When he's not climbing mountains, the 11-year-old spends time doing outreach within the Duchenne community and working to spread awareness.
"He's spoken with the boys with Duchenne and played with them, and he's appeared at our events speaking on behalf of them," Debra says. "Just to see him develop and grow up so fast, he's kind of an old soul to start with, very mature, very responsible, very thoughtful and just an incredible kid."
Donations to Tyler's Climb to Cure Duchenne can be made here.