The boy was hit while standing outside a branch of McDonald’s at around 11.10pm last night.
Police said a motorbike carrying “a number of people” drove past and a weapon was fired.
The boy was hit and a second person, a man aged around 20, suffered minor injuries and was released from hospital.
The victim was taken to hospital for surgery. His injuries are described as potentially life-changing, but not life-threatening.
Police said they are treating the shooting as an attempted murder and have launched a major investigation.
Police want to hear from anyone who may have dash cam footage from the area.
Det Insp Harjit Ubhi, from Force CID, said: “This was an appalling and reckless attack in a part of the city centre which was busy with people enjoying nights out.
“We are already going through CCTV and identifying witnesses, and are determined to bring the people responsible to justice as swiftly as possible.”
Anyone with information has been asked to contact police via Live Chat at west-midlands.police.uk, via 101, or Crimestoppers anonymously on 0800 555 111.