The psychological condition know as Grumpy Old Man Syndrome (GOMS) has been known for many years. Until now however its cause has been unknown. Thanks to a recent scientific breakthrough we now have the answer.
What scientists have found is that we are all born with an innate capacity for absorbing a matter known as bull shit. While there is a large variation between individuals females have a far larger absorption capacity - further research is being carried out to try and understand this gender variation. That which we take in is offset to some degree by a leakage factor, although in most cases we can fill up much faster than we can drain off.
What this means for each of us is that at some point we reach our individual Bull Shit Threshold Limit (BSTL). At this point we can't absorb anymore BS. This is manifest in different ways, but common symptoms include cynicism, grumpiness and a general revulsion at the sight of the moving lips of politicians.
Researchers have also found that among those considered to be at significantly higher risk of developing GOMS are military veterans with a direct correlation between severity of symptoms and length of service.
As any military veteran can attest, the military runs on BS. In fact, it oozes the stuff. This is not normally a problem for recruits nor for some years later. Many who have given long service will tell you they have no regrets about their decision to join and stay. However, a common factor among these veterans and their decision to leave the service is the point came when they reached their BSTL.
Given that many of those who join the military do so at a young age and that there are very few who reach 20 years service you can understand that if you know a military veteran you should not be surprised that they have demonstrated symptoms of GOMS from a comparatively young age.