You start investing intelligence and effort where it really counts so I'd say most younger people I worked with are extremely inefficient but hyper-energetic and willing to waste time and energy on insignificant problems.
This is necessary for education of course but it's often times not contributing to a business' bottom line.
More mature people are almost universally more valuable for a business.
It drops only by a couple of points, and you can lessen the drop with regular physical excercise. I'd say that experience and lifelong education overcompensates for it.
However, I'm sure it's more than compensated for by experience.