Worse, if you've found the information through a Veronica search on Gopher, you may have no idea where the information came from and no sure way to tell someone else where to find it. Since it's critical that readers of a research paper be able to check the sources for themselves, Gopher information without a clear author and search path won't work for serious research. With TurboGopher, you can sometimes get information about a file you're interested in. Pull down the Gopher menu to Get Attribute Info. You'll note it also gives the date on the Mod-Date line.
Many Web pages have a line at the bottom saying when the page was last updated.
Since the Web was not widespread before 1992, with or without a date, the page is unlikely to be more than a couple of years old. How old the information is, of course, is another matter. Mailing lists and newsgroups have the date at the top of the message. Look at the Author Most mailing lists will have the author's name at the top of the message, as will newsgroups. Who's Who , Social Sciences Citation Index , Humanities Citation Index , or Contemporary Authors , or asking the librarian or knowledgeable person in the field.