I see several analogies with "A Generation Removed" by Gary K. Wolf although it doesn’t fit your description 100%.
In this short novel, published in 1977, the US are ruled by the young people and, as long as they're young, they are also allowed to do anything they wish: people are young up to the age of twenty.
As soon as they turn twenty they become adults and are tolerated as active population until the age of 55: at that point, old people keep being checked up even by mobile units on the streets and, as soon as they aren’t healthy anymore, they are euthanized on the spot.
Or just burned in fire chambers as a show for the young people’s delight.
The main character is a 51 year-old cop who's been assigned desk duties due to his age: but suddenly his Captain (even by name) puts him to active duty again, to infiltrate the resistance network, made up of old farts who keep fighting the young rulers.
Once accepted by the resistance, he realizes they are the good guys and joins them actively, de facto turning on the police: but Captain already knew he would betray them and lets his deputy hunt him until the final showdown.
There are no red hands involved but people over 55 must wear a black band to the arm.