Older Profs create a bottleneck...

http://chronicle.com/article/Professors-Are-Graying-and/131226/?sid=at&utm_source=at&utm_medium=en

But many remain productive...

http://chronicle.com/article/Exploding-the-Myth-of-the/131225/?sid=at&utm_source=at&utm_medium=en

So tough luck, kiddies.