By the time swimmers are 22, they are considered to be almost ancient, because there is always some 16 -18 year old to come out of nowhere to blow you away. Is that due to the hormonal and growth changes of a woman's body as she ages, which comes on rapidly compared to a man's body?
At the age of 16, Katie blew away the swimming world. Now at the age of 22, there is an 18 year old Aussie who is starting to mow her down.
Swimming requires a lot of flexibility, and a woman loses a lot of here flexibility as soon as she turns 20 compared to her teen years. This is why gymnasts have an even shorter shelf life of competing at a high level: 14-18. After 18 they are considered to be grandmothers. Biles was 18 in the last Olympics, so I'm sure there will be some, young flexible gymnast to take over in 2020 olympics.