I too go back to Hornchurch, c.1950, but for those who might be interested, the British Army accepted childhood commissions in the 17th century. It was a method by which an officer, who had given meritorious service, could be rewarded by a commission for his son at little cost to the State.
The youngest was supposedly aged 12 months. The practice died out with a four year old, born 1696, commissioned as an Ensign in 1700, aged just 4.
For those who wish to follow it up further:
Notes & Queries, 8th Edition, Vol. VIII, Nov.30th, 1895.