Paul Romer is interviewed in From Poverty to Prosperity, an excellent new book from Arnold Kling and Nick Schulz. When asked about threats to progress Romer says the following:
One factor that does worry me a little is the demographic changes. Young people, I think, tend to be more innovative, more willing to take risks, more willing to do things differently and they may be very important, disproportionately important, in this innovation and growth process.
And then he gives an example of his worry in practice:
…instead of young scientists getting grant funding to go off and do whatever they want in their twenties, they're working in a lab where somebody in his forties or fifties is the principal investigator in charge of the grant. They're working as apprentices, almost, under the senior person. If we're not careful, we could let our institutions, things like tenure and hierarchical structures and peer review, slowly morph over time so that old guys control more and more of what's going on and the young people have a harder and harder time doing something really different, and that would be would be a bad thing for these processes of growth and change. I'd like to see us keep thinking about how we could tweak our institutions to give power and control and opportunity to young people.
Here is a graph from Jason Hoyt showing how much the average age of NIH grant recipients has already increased.