There is typically no statute of limitations on sexual crimes
Wisdom is correct, the law differs in Minnesota.
In Minnesota: Unlimited time ONLY if DNA was collected. (Not sure what they do if DNA collected has degraded because it wasn't preserved properly.)
Statute of Limitations for Sexual Assault Offenses
Minn. Stat. § 628.26
(f) Notwithstanding the limitations in paragraph (e), indictments or complaints for violation of sections 609.342 to 609.344 [criminal sexual conduct (1st, 2nd, and 3rd degree)] may be found or made and filed in the proper court at
any time after commission of the offense, if physical evidence is collected and preserved that is capable of being tested for its DNA characteristics. If this evidence is not collected and preserved and the victim was 18 years old or older at the time of the offense, the prosecution must be commenced within nine years after the commission of the offense. .. .
(n) The limitations period contained in this section shall not include any period of time during which physical evidence relating to the offense was undergoing DNA analysis, unless the defendant demonstrates that the prosecuting or law enforcement agency purposefully delayed the DNA analysis process in order to gain an unfair advantage.
Criminal sexual conduct with a minor: 9 years after commission of the offense or within 3 years after the offense was reported to authorities, whichever is later
Criminal sexual conduct: 3 years
http://victimsofcrime.org/docs/DNA ...sault-check-chart---final---copy.pdf?sfvrsn=2