Going by blog posts, 1.17 was released 2019-12-09, 1.18 was released 2020-03-25, 1.19 was released 2020-08-26, and 1.20 was released 2020-12-08 (today). Great cadence.
AWS EKS seems to support major versions six or seven months later. Support for 1.17 was announced 2020-07-13, 1.18 was announced 2020-10-13. I'm guessing we can plan for 1.20 support on EKS around June of 2021. No judgement, just an observation.