Top brass have raised the top age for recruits by seven years to 33 to counter their desperate shortage of personnel.
The last time the limit was that high was during the last days of the British Empire 59 years ago in the aftermath of World War Two.
Amazingly it means soldiers who join up on a normal 22-year engagement could be fighting just five years ahead of their 60th birthday.
Defence officials last night insisted the move was to harmonise rules across all three armed forces.
But critics claim it is an emergency measure that reveals the true depth of the numbers crisis facing top brass.
The Sun revealed yesterday how the infantry — now short of as many as 2,800 soldiers — is facing its worst manning problem in modern history.
Some 38 out of the Army's 39 bayonet battalions are short of men. Each unit is down an average of 74 soldiers, or a quarter of its fighting strength.
Overworked troops are leaving in droves, saying they are unhappy with poor pay, slum accommodation and too much time away from their family.
Across all the armed forces, the MoD are more than 6,000 below strength.
While the Army has capped recruitment at 26 years, 11 months, the Royal Navy and RAF limits have long been set at 33 due to their less physical jobs.
An Army policy review was prompted by new age legislation last October.
In its findings, published in an internal Army document and seen by The Sun, chiefs said: "There is a lack of convincing evidence to support a case to continue with current differences in policy.
"There is little confidence that current restrictions are either sensible or helpful in manning the Army."
Tory MP and ex-Army officer Patrick Mercer said: "This may be a sign of our sad times, but it is very sensible. Anything that improves the terrible crisis recruiters are facing must be good."
The new limit, confirmed by the MoD last night, counts for all cap badges and trades. Army musicians are the only exception, where new recruits can be 36 years, 11 months.
The minimum age to join up will remain at 16½, with troops still unable to go to war until they turn 18.