"When we were 17 years old we worked for the same ambulance company. I think that at one point we even made pizzas together probably when we were about 15."
Mark Kelly adds that the two also embarked on parallel careers.
"We both became pilots in the navy flying off of aircraft carriers. I flew the A-6 Intruder; Scott, the F-14 Tom Cat and later became test pilots and a lot of test pilots become interested in the space program."
They both began astronaut training in 1996. Since then the men have made multiple space flights, but never together.
Scott says beyond the publicity surrounding their flights - with all those references to the Gemini twins of the ancient Zodiac signs, the brothers know there's work to be done.
"Our focus is completing this mission, doing it successfully. We understand this is a human interest story, but you know our primary focus is doing the job and getting home safely."
While some critics warn that its shutdown could pose access and supply problems for the International Space Station, Endeavor commander Mark Kelly says it's time for the Space Agency to retire the shuttle and chart new directions.
"The shuttle was designed to build a space station and after STS-134, the International Space station will be complete. It has really done its job," he says. "And in order for us to build a new class of rockets and a new spacecraft and to do other things, we are going to have to retire the space shuttle."
Scott and Mark Kelly say their work in space has been a privilege and both feel it's been an honor to serve their country through the space program. They say their numerous trips to earth orbit have given them a new perspective on the planet.
Scott says, when he looks down on earth from space, political borders disappear. "It makes an impression on you that we are all part of planet earth."
Mark agrees. "The atmosphere is a little sliver that is pretty thin and fragile. You think about what we all need to do to protect it."
When the Kelly twins finally do meet in space next year, crewmembers are not likely to have any problem telling the two identically bald-headed brothers apart. Mark says he'll still be wearing his signature mustache.