In the world of sports stadiums, 20 is the new 30.

Stadiums are typically financed through bonds that take 30 years to pay off. But their useful life isn't always that long.

Just take last month’s announcement that the St. Louis Rams would be decamping to Los Angeles, leaving behind its 20-something football stadium for a shiny new one. The St. Louis Regional Convention and Sports Complex Authority is still paying off a portion of the $259 million in bonds it issued to build the Rams a new stadium when they moved from L.A. in 1995.

It's not the only issuer paying off 30-year debt for a project that didn't make it the full life of the bond. In Georgia, the Atlanta Falcons are moving to a new stadium next year even though the Georgia Dome is less than 25 years old. The San Antonio Spurs left the Alamodome in 2003, just 10 years after it was built.