Because I'm quite new in this group, I'm reading archives and sometimes find interesting questions. Some of them already have answers, some -- also accepted answers. But I feel I can answer in another way, but I'm not sure if it is ok to say anything half a year or more for such a question.
I highly recommend answering old questions, because it helps develop the body of knowledge for that question, and it helps you become more comfortable with the site. By answering old questions it creates another opportunity for the community to review the question, and answers, for errors, etc.
Personally, I like to use the favorite function to mark questions that I intend to answer at some point, because I never know when I'll have the time to sit down and devote the time I want to answering a question.
The caveat is of course that you have to have something new to add to the question.
If you have something useful to add to the answer domain of an old question, please do so.
If you do it well, there's even a special badge for you: Necromancer