That act is prohibited by law.

His action is unforgivable.

Smoking is prohibited in this park.

Smoking is banned in this park.

He has not yet reached the legal age.

He obtained that position by using force.

He was arrested for committing a criminal act.

He thought deeply about the result of that juristic act.

He is still a minor, so he does not have full capacity to act.

He avoided talking about actual sex acts with her.