I only first tried out porn when I was close to 40 and got kind of hooked. I have begun to understand its negative effects from a number of things I have read online and am now working towards breaking the dependency.
There is no obvious way to stop this except to develop the mental strength to just say no. In addition it is a good idea to think about it and develop some specific activity that is an alternative to watching porn (got this from another website). The most important thing is that you should enjoy the other activity - and it should not itself be a negative activity (so it can't be taking drugs :-))
It could be exercise, it can be taking a walk, cooking, reading, anything. But it should be something that you enjoy. And as soon as you develop the urge to watch porn, drop what you are doing and do that other activity. If you enjoy it you will eventually forget the porn. Great choices are maybe visiting someplace outside your house (like a park or a gym) or calling a friend, etc. Because that completely removes you from the temptation.
It will take many months, maybe even a year but eventually you will be able to fill your life up with enjoyable things without needing porn.