In the real world, it is really a problem and has its official name too, like irritable male syndrome. What causes this? There are many reasons the Kraken comes out of the man you care for or a neighbor you know or maybe the aging boss. the number one reason may be health related as the body changes in men just like women. Let's face it men lose their hair get a belly and even grow some manly boobs. All that can make you grumpy for sure.
Another reason could be loneliness. When you are alone it can get very depressing and the downfall on that is the more alone you are the grumpier you will become.
But this is also true:
They were grumpy young men, and they got old. They're a minority, you know. Most old men are perfectly nice, and some have even mellowed with age. But some have been rehearsing all their lives for this role.
Of course, when they were young they called it something cooler. Sulky, maybe. A little sullen. Over-critical, perfectionistic.
Then in middle age, they got irritable, even disgruntled.
And finally, after years of practice, they reach their full potential.
Voila! Grumpy old men!
Get off their lawn.