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.
Karena ia melihat sekelilingnya dan ia melihat semua ahli fisika hebat ini yang menemukan mekanika kuantum dan fisika modern, mereka semua berusia 20-an dan awal 30-an saat mereka menemukan hal-hal itu.