A first-time offender in Pennsylvania is as the name references a person who has not been in trouble before has not been say convicted of a criminal offense. A first-time offender, it may be a college student, a working person, a professional, someone who could be even advanced in age who has not found themselves on the wrong side of the law, or who has made a mistake and got into trouble.
Who a first-time offender maybe can, of course, vary. It is slightly more nuanced in the sense of a person can possibly be considered a first-time offender if their criminal conviction was far enough back and would be otherwise appropriate to the circumstances in the sense of seeking consideration as being a first-time offender. When the term first-time offender generally rises is for people who have been arrested or trying to avoid a conviction and would be seeking some diversion for the court, say either through the ARD program, Accelerated Rehabilitated Diversion, or some other diversion program or potentially an alternative resolution that would be negotiated by the defendant's attorney.
Having an experienced Pennsylvania criminal defense attorney in your corner from as early as possible in the process is going to be able to help you understand and navigate the process as best as possible especially for a first-time offender where even more is at stake.