Yes, we are actually discussing a rather wide range of issues here, age of consent to marry, the statutory definiton of consent, federally versus state mandated ages, and the point of the famous New Yorker cartoon "on the internet nobody knows that I am a dog". However what is probably closest to the orginal question has to do with "age gap" and state laws concerning, most particularly, sexual abuse of children.

In most states consensual sadomasochistic sexual relationships between two individuals older than 15 or 16 with a less than three year age gap between the two individuals will not usually bring the DA or States Attorney General down on the individuals. This is, of course assuming that no physical injury results and neither individual is bringing charges against the other (in which case we are looking at sexual assault or physical assault). This activity would be considered to be exploratory sexual activity between peers.

On the other hand, in most states, a seventeen year old having a sadomasochistic sexual relationship with a twelve year old, would upon the matter being brought to the attention of the authorities, result in an investigation and the possibility of charges being brought by the state authorities under sexual abuse of children. Individuals who are legally children (e.g. generally under 18) can be prosecuted for sexual abuse of children. In most cases the critical "age gap" is three years. Again in most states, adults in a professional role or adults in significant positions of authority are required to inform the state child protective services when the possibile occurance of physical or sexual abuse of children exists.

In general, there is operationally the same three year "age gap" functioning between an 18 year old and a 17 year old whereas a 17 year old and a 21 year old breaches the 3 year rule.

Surprisingly, there is a significant amount of common sense in the enforcement of this. However, in Texas if a 18 year old male knocks up a 13 year old girl (which happens quite frequently) he may be looking at more than child support. It all depends on how the local prosecutor feels that week. An important principle is, the interest of the law enforcement authorities is usually directly proportionate to the severity of the injury inflicted and the publicity of the event. Make sure that experimentation does not cross the line over into assault. It is far too easy for what was consent last night to become force once the buises appear. Best to confine ones efforts to one your own age group and wait until one has reached their full legal majority before engaging in activities that might twitch the interest of the DA.

Fortunately, in works of fiction we are not so limited or Mr. Nabokov would have to confine his writing to butterflies.