Well, because he looked around himself and he saw all these fabulous physicists that created quantum mechanics and modern physics, and they were all in their 20s and early 30s when they did so.
Parce qu'il a regardé autour de lui et a vu tous ces fabuleux physiciens qui créaient les mécaniques quantiques et la physique moderne, et qui avaient tous la vingtaine et une jeune trentaine.