Acceptable is some piece of text that you composed and typed with your own two hands, and is now still publicly accessible – you could give someone a URL and they could see it.
The oldest I can find for me is a fairly lame newsgroup post I made on December 16, 1988.
I wrote these sometime before 1994 or 1995, though these specific posts are from 2001.
Ten pages into Google and the oldest thing I can find is from 1994. I know I had some stuff up there from 1993, but I cant track it down right now.
3/14/94 on alt.callahans newsgroup.
I wrote a bunch of articles about how various computer buses worked around 1996 and 1997 or so. Most of those are still floating around the net. Some of them were later published in books.
ISA
EISA
http://www.embeddedlinks.com/chipdir/oth/sokos/eisa.txt
VLB
Multibus
A searching in google groups reveals a terrible* usenet post from January 1995. Since my first internet access was just a few months before, I wouldn’t be surprised if that was indeed the oldest.
*It is a tad dickish, pretending not to understand someone’s typo, and it adheres to Gaudere’s law
“Take my wife… PLEASE!”
My first patent was mid 1980s and it’s out there. Of course, I didn’t write it there.
I was really active on Compuserve starting in 1991 when I bought Internet in a Box and found a 1200 baud dialup. Maybe that stuff’s still out there?
Probably messages I posted on a Compuserv forum (for professionals in my trade) around 1995. I’m assuming stuff like that is still moldering somewhere on the innerwebs.
My bachelor’s thesis from 1977 and an article I published in 1979 are both on the Internet, although they didn’t start there. But they’re still “the oldest things I wrote that are still on the Internet”.
Of the things I wrote directly on the Internet, my oldest thing might be my first post to the Dope Board in May 2000
I wonder if anything from the old PLATO system ever got archived on the net. If so I’d go back to about 1979 or 1980, I think.
I have been posting on Usenet since 1991 or so and that stuff is archived so that.
I have an Amazon book review from December 1999 that’s still up.
I was active in Yahoo groups and similar in the same time frame. I have no idea if any of those things are still around or archived somewhere.
I’ve got lots of stuff from 93/94 that’s still active on a few sites. I know there’s stuff on some of the newsgroup archives from the late 80’s.
I contributed to this survey report on public opinion in Ukraine: https://www.ifes.org/surveys/public-opinion-ukraine-1999
I’m pretty sure there are some Usenet posts from late 1991 or early 1992 floating around, but the oldest ones of mine I could find quickly are from October 1993 (alt.bbs.pcboard).
Probably best I can’t find the older posts - I can’t imagine the cringe factor…
Maybe not exactly what you’re looking for, but this UIUC PLATO archive exists.
The first academic paper I wrote was published in 1975. It is available on Jstor. When it first was put into Jstor I have no idea.
A Slashdot AMA.
Probably the 1994 post on alt.fan.cecil-adams where I inquired about the female equivalent of the euphemism “spanking the monkey.” In think the thread title was “Spanking the Monkey = ?