The is no age requirement regarding merely dating. This means that a 16 years old can generally consent to have sex with any adult, regardless of age.

Is it wrong for a 16 year old to date a 27 year old?

The answer is yes; however, because the 16 year old is still a minor, if she is doing things she should not be doing he could be charged with contributing to the delinquency of a minor.

Is it OK for a 21 year old to date a 16 year old?

Generally, it is not illegal for these two to date. Of course, any sexual activity is considered statutory rape, but if there is no sexual aspect to their relationship, then they are probably fine. However, this is a fine line to walk for the 21 year old.