In my experience, if the question is really old the original author won't respond even if you comment (or they'll say something like "yes, things are different now, this was written in 2015"). And if it's really outdated you'll sometimes see someone else replying with the more up to date answer anyway. Commenting on old answers is seldom helpful, in my experience.

About the only use I see for comments is asking for clarifications or pointing out an obvious mistake in relatively recent answers.