yakusha no tamago
an egg of an actor
an unfledged actor; a budding actor; an aspiring actor; an actor in the making
Similarly, you can also say 医者の卵 (an egg of a doctor), 研究者の卵 (an egg of a researcher), 弁護士の卵 (an egg of a lawyer), etc.
Because he is still an actor in the making, he works part-time at a convenience store to make ends meet.