Can a 16 year old date a 20 year old in California?

As you seem to be aware, non-sexual dating would be legal in California between a 21 year old and a 16 year old. There might be exposure under other laws such as contributing to the delinquency of a minor but no unlawful sexual

Can a 16 year old date a 20 year old in Louisiana?

There is no definite age of when a minor may consent to sex in Louisiana. Instead, it varies depending on a few factors, such as the age of both parties, and the age difference, if any, between them. However, a person 17 or older can consent to have sex with a person of any age.