yes there is a statute of limitations for your "friend". Just stay clean and then you don't have to worry.
This is just my opinion and not a comprehensive answer. You assume the risk because this answer may not apply to your situation depending on the facts.
Your friend needs to consult with an attorney who will be able to ascertain what particular charges he could potentially face after knowing all of the facts. From there, the attorney will be able to advise what the SOL would be for each possible offense. Most felonies that have a punishment potential of less than 8 years have a 3 year SOL. But particular sex crimes have a 10 year SOL per California Penal Code 801.1.
Whoever is concerned about potential charges being filed, particularly these type of charges that can have long lasting consequences, should retain an attorney during a pre-file investigation stage of the case.