Why old people die after a fall

It is well known that elderly people fall, break a hip, get pneumonia and die.
BUT WHY?
Younger people fall, break a hip and get better.
There is a branch of science that studies ageing  - called gerentology.
They have discovered that when something traumatic happens to you - such as breaking your hip -
it causes 2 chemicals to be produced in your blood.
These nicely balance each other.
When you are over age 60 and you have that same trauma -
it causes lots of 1 chemical (cortisol) to be produced
but
the ageing person can't make enough of the other one (DHEAS)
Without the balance of that second chemical, the first chemical reduced the persons ability to fight infection
So
You get pneumonia or MRSA
and die
The gerentologists are pushing for all hospitals to have the second chemical (DHEAS) available to be given to all trauma patients over the age of 60