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.