Barrayar is a planet where you're either military or you're nobody. When his father asks what will 17-year-old Miles Vorkosigan do now that he's flunked the military academy physical test through a foolish mistake, “Miles lips tightened and he shrugged. 'There never were any alternate plans. I'd planned to succeed. More fool I.'”
So Miles goes off to visit his grandmother on Beta Colony and there tries to help a couple of men whose futures seem even more hopeless than his. This leads to purchasing a spaceship and contracting to deliver a cargo of weapons to a planet at war. The hyperactive plot dashes from crisis to crisis as Miles gets in further and further over his head. But for Miles, poisoned before birth with a chemical that stunted his growth and weakened his bones, this is a fresh chance to be a warrior. He just hadn't expected to have all these people depending on his leadership.
Sequels to The Warrior's Apprentice follow Miles' life as he juggles his role in the aristocracy of Barrayar with the off-planet responsibilities that resulted from this adventure. One was reviewed here previously. If science fiction about persons with disabilities interests you, Ann McCaffrey's The Ship Who Searched tells of Hypatia Cade, paralyzed by an alien virus, who becomes a spaceship with all its circuits connected directly to her brain.