This, of course, depends on jurisdiction. In Spain, for example, the age of consent is 12. In the Netherlands, it's 16, but between 12 and 16 only the person involved or eir legal representatives (parents, legal guardian, or presumably someone with power of attorney---I don't know Dutch law) can report you to the authorities. In Kentucky, it's 16, or 14 if you're under 21. In many jurisdictions, though (for example, Arizona), the age of consent is 18. In Trinidad and Tobago, it's 21. In too large a number of jurisdictions, it depends on the sex of the potentially-underage person (usually being lower for females: everyone knows those awful 20-year-old jezebels are trying to seduce our boys; but we have to let the girls get pregnant early, or they might---*gasp*---get a job and challenge the patriarchical status quo).

For more information, see the informative and (perhaps) useful

Also, the punishment for statutory rape of someone close to the age of consent is usually not so steep as twenty years. Now, for 5-year-olds, perhaps.