For the first nine months of his life, Matthew Cech was the healthiest of babies. But that quickly changed when his parents, Terry and Lisa, noticed how bloated their little boy’s stomach would become throughout the day.

After numerous visits to doctors and trips to children’s hospitals around the country, Matthew was diagnosed with mitochondrial disease, an extremely rare and fatal condition, at 3 years old.

According to the United Mitochondrial Disease Foundation, mitochondria are responsible for creating more than 90 percent of the energy needed by the body to sustain life and support organ function. When mitochondria fail, there is less energy within the cell, which leads to organ system failure.

“We were told that 80 percent of children diagnosed under the age of 5 won’t live until they’re 20,” Terry, 49, of Plattsburgh, New York, tells PEOPLE. “But we don’t focus on the bad because if you focus on the bad, bad things will happen. He is not going to be the 80 percent that die.”

Mitochondrial failure can happen anywhere in the body, and for now-13-year-old Matthew, it’s affected his stomach. This has left him unable to eat solid food.

Instead, Matthew uses a 24-hour feeding tube but still weighs just 51 pounds.

Eating solid food is so dangerous for Matthew, his parents say, that after indulging in just one potato chip during a field trip last year the teen had to be hospitalized.

“Even though I know I can’t eat, seeing everyone eating, and smelling the food is just so tempting,” Matthews tells PEOPLE. “I can’t participate in gym class. I can’t play outside for hours. I have to come in and take breaks or cool off.”

But despite his illness and every day struggles, Matthew — who has had countless surgeries throughout his life — says he “doesn’t look down.”

Instead, he adds, “I look at all of the things I’ve been able to do.”

One of those things involves his alter ego — which he calls Mighty Matthew.

“Mighty Matthew is a superhero who is not afraid of anything,” he says. “He can never run out of energy. He can take the bad energy from people who don’t deserve it and give it to the kids that need it. When I put on the suit, it makes me happy because I’m making other people happy.”

Matthew, who just started his freshman year of high school, is focused on educating his community about his condition and has helped put together fundraisers to raise money for research.

Today, everyone from his parents and his older brothers, Bradley and Steven, to doctors, are in awe of how far he’s come.

“Study after study show that if you go in there with a positive attitude, regardless of what illness you’re fighting, you have a much better outcome,” says Terry.

Adds Lisa, 45: “No matter how bad of a day it is, there is always something good in it. You can always find some little bit of hope.”

Matthew, known for his great sense of humor, is able to live his life despite his prognosis. He’s a registered member of the Plattsburgh State baseball team, and although he can’t play, he goes to their practices, games, and even has his own locker.

He spent his summer playing badminton, running around outside, and like always, giving out advice to others who are going through a hard time.

“It will get better eventually,” he says. “You just have to be positive. Hope will always come through for you.”

To make a donation toward Mitochondrial Disease research, visit UMDF.org or MitoAction.org