its illegal
I think an abstinent relationship is legal anywhere between anyone.
the age of consent in the US state of Tennessee is 18, so such a relationship would likely be not legal
Depends on the age of the girl and the state you are in. If she is 17 or under, there could be problems in many states.
With a sexual relationship, no it is not legal.
Statutory rape, regardless of consent. The boy is a 'legal' adult in every state, and the girl is well below the legal age of consent in every state.
as long as their relationship does not involve a sexual relationship otherwise, you should check the laws in your area to see if it is legal
The relationship itself would not be illegal. People of any age can date legally; however, if the relationship is advanced to a certain intimate level, then it becomes illegal.
It depents on the country you are from
It is not illegal.
If he can prove that they were having a sexual relationship when the girl was not of legal age, but the boy was, then yes he can try to take legal action against the boy.
Dating is not legislated. However, dating leads to other things and any sexual contact between the two would be considered illegal.
It may be ok to "date" a 17 year old, but having a sexual relationship with her is illegal and is called statuatory rape.