Sounds like the Insignia trilogy by S. J. Kincaid; first book was released in 2012.
More than anything, Tom Raines wants to be important, though his shadowy life is anything but that. For years, Tom’s drifted from casino to casino with his unlucky gambler of a dad, gaming for their survival. Keeping a roof over their heads depends on a careful combination of skill, luck, con artistry, and staying invisible.
Then one day, Tom stops being invisible. Someone’s been watching his virtual-reality prowess, and he’s offered the incredible—a place at the Pentagonal Spire, an elite military academy. There, Tom’s instincts for combat will be put to the test and if he passes, he’ll become a member of the Intrasolar Forces, helping to lead his country to victory in World War III. Finally, he’ll be someone important: a superhuman war machine with the tech skills that every virtual-reality warrior dreams of. Life at the Spire holds everything that Tom’s always wanted—friends, the possibility of a girlfriend, and a life where his every action matters—but what will it cost him?
The premise of the story is that there are 2-3 main coalitions on Earth and they fight over resources in the edges of the solar system with spaceships that are controlled from Earth by kids with computers in their heads.
Tom stopped twirling the virtual pencil and tried to concentrate. “Modern wars aren’t fought by people. I mean, they’re kind of fought by people, because people on Earth control mechanized drones remotely, but the machines do the actual fighting. If our machines don’t get demolished by Russo-Chinese machines, our country wins the battle.”
“And who is involved in the current conflict, Tom?”
“The whole world. That’s why it’s called World War III.” She seemed to be waiting for more, so Tom ticked off the major players on his virtual fingers: “India and America are allies, and the Euro-Australian block is aligned with us. Russia and China are allies, and they’re supported by the African states and the South American Federation. The Coalition of Multinationals, the twelve most powerful corporations in the world, is split down the middle between our two sides. And … yeah. That’s about it.”
The reason they need kids for this has something to do with brain elasticity and putting computers in adults causes them to go mad.
It turned ugly for us adults, but don't worry it's perfectly safe for you.
“All the trainees undergo the procedure, Tom. It’s safe.” Marsh’s eyes riveted to Tom’s forehead. “What you teenagers have in great supply—and we adults do not—is neural elasticity. Your brain’s adaptable. Adults and neural processors don’t go together. We tried it, and it turned ugly. Adult brains couldn’t adjust to the new hardware. So we use teenagers.”
The best fighters from each side of this conflict were something of superstars.
Well, there's quite the description of Elliot Ramirez, Indo-American hero.
Elliot Ramirez was everywhere. Everyone knew him—the handsome, smiling, all-American seventeen-year-old who represented the future of Indo-American supremacy in the solar system. He was in commercials, on bulletin boards, his bright grin flashing and dark eyes twinkling on cereal boxes, on vitamin bottles, on T-shirts. Whenever a new Indo-American victory was announced on the news, Elliot was trotted out to give an interview and to talk about how America was sure to win now! And of course, Elliot was front and center in Nobridis, Inc.’s public service announcements because they sponsored him. He was one of the young trainees who controlled American machines in outer space, one of the Americans dedicated to taking down the Russo-Chinese alliance and claiming the solar system for the Indo-American allies.
Found with the Google query
tom spire mars site:goodreads.com