What would the law say if an 18 year old boy were to be sexually active in Idaho with a 16 year old girl? Is it lawful?

According to Idaho statute chapter 61 title 18, it is unlawful for an 18 year old to be sexually active with a 16 year old.

"Rape" is defined as penetration, however slight, of the oral, anal, or vaginal opening with the perpetrator's penis accomplished with a female under any one (1) of the following circumstances:
1. Where the female is under the age of eighteen (18) years.
The statute lists a total of seven (7) circumstances this being #1.