What about for a female at her early 20?
In common, it is recommended to do a health check up in every 2-5 years for a female from the age of 25 to 30 depend on the first condition after the first check up and different types of screening test. Anyway, It's best to do as early as you can. And the Doctor will recommend you the suitable screening tests that should be done in your age.
Normally, health check up can be done without any noticeable symptoms as it helps to detect any health concerns early. And for the frequency of the test is based on the difference of each individual such as age , sex and health condition.