I had heard the term "old fart" used disparagingly since as far back as I can remember but I didn't know why "old and "fart" went together but I was never short on imagination. My *final conclusion* as a kid of about six or seven was the result recalling a kind of "fecal" odor that I often smelled when my granduncle (Who was *very* close to me and took me absolutely everywhere with him right up until his death -- just one week before my 9th birthday.) stopped to chat up some rather elderly men, some about his age, most were older. Although my granduncle himself had no such odor I suddenly had the thought that when people got very old, especially men, they couldn't control their bowels very well and no longer could wipe their bums very effectively.Thus, the term "old fart" suddenly *made sense* to me!
I believed this for a very long time and I still don't know the *actual* origin of the term, "old fart."
A childhood belief about farting

others believed things like this
- when i was a little girl, i beleived that women didnt have bums, because i never heard my mom fart. Anon
- I used to think when you smelled a fart, that you were breathing in tiny pieces of poop.— brandypandy
- Pink Floyd- Brick Wall.
I used to believe it was "we don't need no fart control" in the second line there.— Norwegian Dude From Kopervik - I used to believe that my grandpa had a special power that made him fart each time I pulled his finger. — confused
- I used to believe that if you had to fart and held it in too long that it would cause you to blow upAnon
- I used to believe that if you held a fart in long enough it would come out as a burp.— Chris