Incorrect.
In both the British military and the US military, the age of the officer is irrelevant. Date of rank is all that counts.
This detail comes to light in the film, "Zulu," when lieutenants Chard and Bromhead unzip their trousers, pull out their wedding tackle and compare ... dates of commission. Since both are still just entry-level commissioned officers (meaning neither has received their first promotion), date of rank and date of commission are the same.
It is pretty much a universal military tradition that someone is always in charge, and that someone is the senior ranking individual present, regardless of rank. Which might be a Private First Class being in charge over a bunch of privates E-1 or E-2.
In protracted wars it is not that uncommon for an enlisted man (what the British call "other ranks") to take command because all the officers have been killed or wounded but otherwise rendered combat ineffective. But someone is always in charge.
“””””It is pretty much a universal military tradition that someone is always in charge, and that someone is the senior ranking individual present, regardless of rank. Which might be a Private First Class being in charge over a bunch of privates E-1 or E-2.
In protracted wars it is not that uncommon for an enlisted man (what the British call “other ranks”) to take command because all the officers have been killed or wounded but otherwise rendered combat ineffective. But someone is always in charge.””””””
You gave another good description, someone is “always in charge”.