I've updated the original post, four more players broke Top 100 after the Australian Open. I'll update the new career high rankings for the other players soon.
Donna Vekic (CRO): 16y7m0d - 1996 (#93)
Madison Keys (USA): 17y11m11d - 1995 (#81)
Jana Cepelova (SVK): 19y7m30d - 1993 (#97)
Kristyna Pliskova (CZE): 20y10m7d - 1992 (#85)
Really impressive for Vekic