Is it illegal (statutory rape) for a 14 year old boy to have consentual sexual relations with a thirteen year old girl?

Though it may not be considered "Statutory Rape" in the criminal sense, this is an "illegal" sexual act between two minors. Due to the fact that they are under the age of 18, this would be a matter for a family court judge to rule. A judge would make a determination as to whether criminal action should be taken.

163.315 Incapacity to consent; effect of lack of resistance. (1) A person is considered incapable of consenting to a sexual act if the person is:
(a) Under 18 years of age;
(b) Mentally defective;
(c) Mentally incapacitated; or
(d) Physically helpless.
(2) A lack of verbal or physical resistance does not, by itself, constitute consent but may be considered by the trier of fact along with all other relevant evidence. [1971 c.743 §105; 1999 c.949 §2; 2001 c.104 §52]