Is it bad for elderly men, whose partner can not participate in sex, to watch porn videos? Will they be labeled a pervert?

Frankly if you are doing it in private, it isn't something illegal (children), and you are not putting those types of unrealistic expectations on the relationships in your life....I honestly don't know what the big deal is. You may need to be cognizant of whether it becomes an addiction or is just for "entertainment". Does it control your life?
"Pervert" is technically defined as abnormal or unacceptable. To me, a pervert would be someone who is watching child pornography. There is a line. But if you are an adult and the featured players in what you are watching are adults, I don't think that makes you a pervert.
I think people can be very hard on themselves. And I think we allow ourselves to be prejudged. meaning we assume other people are going to judge us before they are given the chance.
WHO is going to label you? If it is other people, how will they know if you are discreet? If it is you, is that some preconceived notion of what is acceptable?

Given that the majority of porn out there is not very flattering to women you aren't likely to have many in real life cheering you on and if you are foolish enough to indulge publicly then you may very well be labled a pervert, or at the very least a dirty old man. Partaking in virtual sex should be just like having sex with a partner, discreet and private.

What kind of porn are we talking about here? This is the internet! A whole world of wonders awaits the curious. Fire up Google, turn off that Safe Search, and explore!

I don’t mean to be sarcastic but do you plan on having an audience?

If you do this privately, how will anyone else know about it?

If no one knows, who is going to label you? Do you view yourself as a pervert?

Are you asking from a ‘moral’ standpoint? If so, speak to your pastor or another clergyman.