If a person gets into a physical altercation with someone else how long do they have to file charges before it's too late to do so?
The statute of limitations for the state to file criminal charges against a person for assault is usually 1-5 years depending on the charge (i.e. misdemeanor or felony). In the civil system, the statute of limitations to file a civil action for assault/batter is usually 2 years from the date of the assault/battery. If you are assaulted by a person, you need to file the charges that day or the day after so that the incident is fresh and the police can take immediate action and that you can document you injuries with a photograph. I suggest that you press the charge and file a civil action against the person so that you can not only get the person in trouble for their actions, but you can force them to pay you monetary damages.
First of all the prosecutor, not the victim, files charges. As the victim, you would file a "criminal complaint" upon which the prosecutor would make the determination as to whether or not to have charges filed. Since you didn't give much by way of details, I don't know exactly what your criminal complaint would be for. However, the sooner you make out a complaint, the better for your case.
The time limit in which charges can be filed is known as the "statute of limitations". In PA there is a 2 year statute of limitations for minor offenses and 5 year statute of limitations for major criminal offenses. The period begins to run upon commission of the offense.
If you also want to sue in civil court there is typically, a 2-3 year statute of limitations for such cases.