Ponzi schemes can go on for much longer than 12 years. Madoff said that he began the Ponzi scheme in the early 1990s, but federal investigators believe that the fraud began as early as the mid-1980s[18] and may have begun as far back as the 1970s.. He was caught by confession in 2008.

Over approx. 20 years, Lewis collected around $311 million U.S. dollars from investors. https://en.wikipedia.org/wiki/James_Paul_Lewis_Jr%2E

In another ~20 years we can stop calling Bitcoin a Ponzi Scheme, but speculative investment can fuel exponential growth for much longer than you might think.