Children 13 years of age or younger cannot legally consent to sexual activity with anyone of any age. 14-year-olds can consent to sexual activity with partners 18 years of age and younger. 16-year-olds can consent to sex with someone 20-years-old or younger.

Is it OK for a 16 year old to date an 18 year old?

No this is not illegal. Simply dating a person over age 18 is not illegal. It can become illegal for a person who is 18 once sex is involved.