Kingsman Wilkie, from the Second Battalion the Duke of Lancaster's Regiment, was sent to Afghanistan aged just 17 when the standby battalion was called on to reinforce troops in Helmand.
Despite being too young to buy an alcoholic drink or get married without his parents' permission, Adam was able to serve in the battle against the Taliban, according to the Sun.
“It was like World War Two when recruits hid their age to enlist," a source told the newspaper.
“The lad was just desperate to get out there and prove himself. He knew he was underage. Wilkie does look a lot older than his years so no one thought to check how old he was.”
Adam, who is believed to be from the Manchester area, served with courage for the regiment known as the "Lions of England".
The Ministry of Defence confirmed that Adam, now 19, was just 17 years and nine months old when he served in Lashkar Gah, Helmand province.
A spokesman said: “It is regrettable and goes against stated MoD policy. This extremely rare situation was down to human error. The Army has taken action to try to ensure this does not happen again.”