It's not even the longest-lived company in the world. This construction company was founded in 578 AD and continuously operated until 2006 when it was bought by a larger company: https://en.wikipedia.org/wiki/Kong%C5%8D_Gumi
100 years ago was only 1919 -- here are some random companies from 1919 that I found on Wikipedia (ignoring for a moment that this is plainly surviorship bias):
https://en.wikipedia.org/wiki/Champion_(sportswear)
https://en.wikipedia.org/wiki/KitchenAid
https://en.wikipedia.org/wiki/Thrifty_PayLess
https://en.wikipedia.org/wiki/Tesco
https://en.wikipedia.org/wiki/Proffitt%27s
https://en.wikipedia.org/wiki/Bentley
https://en.wikipedia.org/wiki/A%26W_Restaurants
Companies surviving for 100 years isn't quite routine but it's certainly not so rare that its surprising when one does. I don't think it's at all inconceivable that Amazon could stay open for a hundred years. It's made it past the first 10 years, the turbulent start when most companies are culled. I'd wager that the biggest threat to Amazon surviving to 100 is being broken up a la Bell/Standard Oil.
Second, that's average time in the S&P 500 index. As noted and n the report, there are many reasons besides going under that companies drop off the index. That number doesn't really say much about longevity of the company.
Bayer (1860s Germany), Johnson & Johnson (1886), 3M (1902), the Coca-Cola Company (1892), IBM (1911), HP (1939), Mitsubishi (1870), Wells Fargo (1852).