If a 18 yrs old male or female dates a 14 years old male or female, is that considered rape. And if both agree on having a sexual relationship, is that considered rape?

Yes. In the state of New York, a person under the age of 17 is not capable by law of giving consent. This means that even if they verbally consent, under the law it is not valid. See the law below.

§ 130.30 Rape in the second degree.

A person is guilty of rape in the second degree when: 1. being eighteen years old or more, he or she engages in sexual intercourse with another person less than fifteen years old; or 2. he or she engages in sexual intercourse with another person who is incapable of consent by reason of being mentally disabled or mentally incapacitated. It shall be an affirmative defense to the crime of rape in the second degree as defined in subdivision one of this section that the defendant was less than four years older than the victim at the time of the act. Rape in the second degree is a class D felony.