Millennials are now age 15-34. They’re the largest generational cohort in America – 83 million strong.

Baby Boomers are still riding high. They’re age 51-70.

Millennials are having fewer children, and at an older age, while Baby Boomers aren’t quite leaving the workforce and living longer. This means population growth has capped – now in a 20-year decline – the average past-prime income age is growing, and – according to Standard & Poor’s – we are seeing, and will keep seeing, a substantial decline in annual economic growth.

For more, look at this chart, which shows the GDP growth rate nearly leveling off over the past eight years. The recession helped, sure, but taking a step back, this is a combination of evolution and a failure to adapt. Americans are hanging onto an economy stuck in the 1980s, while Millennials haven’t done enough to disrupt the flow.

One major indicator: the energy sector. FT reported earlier in the year that as crude oil demand drops precipitously across the world, the U.S. is finding a shrinking market for drilling equipment. The longer the U.S. relies heavily on traditional energy markets, the worse things will get in the energy sector. Disruption is necessary but isn’t happening at a necessary volume.

A few things could help, S&P continued: Millennials will be making more money as they age, and immigration can help push the economy forward.

Sure, small things. But Millennials need to begin disrupting industries at a large scale. Full energy independence is one thing, but redefining the global energy sector is another. If Millennials can’t become global change-agents for the largest economies, then it should feel comfortable with a static existence and heavy partnerships with booming power economy China, and emerging secondary economy India.