On another note, Ajee Wilson was finishing 5th at Worlds and running low 1:58's at the same age this chick is now.
Wrong. Ajee' Wilson was 19 in 2013 (birthdate is 5/8/94) when she ran 1:58.21. When she was 18, she ran 2:00.91, which was her pr. Efraimson is 18 and her pr is now 2:01.13 and surely will go faster with faster competition this year. Whether she then breaks through to 1:58 and 1:57 the next couple years, like Ajee' did, is uncertain, but she has a good shot at Cain's age 18 best of 1:59.51 from Prefontaine.