That's pretty crazy, but I may actually have that beat!
I saw an add for an item in a magazine that I got in 1989, and I scraped together the money and sent them my order and payment in mid to late 1989. I never got my item, and eventually gave up on ever getting it. I was home from college the summer of 2001, and I was picking up the mail one day. It's just junk mail for my parents, a few random stray bills, and this one yellowed letter with a bunch of postal stamps on it including several "Return to Sender" marks. The address was in my childhood handwriting. It was the missing order, and it only took 12 years to make it back to me!