How much time can go by without pressing charges?

Pennsylvania

I want to know how long it takes for someone to press charges against the other one? Is there only a few years if any?

If I understand your question, you are asking what the statute of limitations is for a sexual offense in the State of Pennsylvania.

JUDICIARY AND JUDICIAL PROCEDURE (TITLE 42)
Any sexual offense committed against a minor who is less than 18 years of age may be prosecuted any time up to 5 years (the period of limitations provided by law) after the minor has reached 18 years of age. This encompasses 11 different degrees of sexual offenses including anything relating to statutory rape.