"The older the scientist you choose to do your Ph.D. thesis with, the more likely you will find yourself working in a field that saw its better days a long time ago, possibly before you were born. Even when a mature scientist still has all his marbles, he often wants to put more bricks into an edifice that already has enough rooms. ... Young professors in contrast are generally hired not for grandeur but because they represent a new intellectual thrust not present in a department, one with hopes of remaining lively over at least the next decade. Moreover, they are likely to have smaller research groups than more senior professors, around whom funds as well as stodgier minds tend to aggregate."