A wizard is an expert magician but there are some trainees (like Sabrina the Teenage Witch). I was wondering if there is a single word to describe an amateur or young wizard as opposed to fully describing as "young wizard".
Since wizard and witch are not typical identities or avocations, at least in the modern English-speaking world, I don't think there is any common term for a newcomer trainee like resident or postulant or rookie.
There may be invented terms specific to various fictional fantasy universes, but in general communication one can expect "wizard" or its equivalent mated with the general terms for newcomers like novice, neophyte, trainee, fledgling, recruit, and so on, as in The Sorcerer's Apprentice.
I wouldn't be sure that a wizard is necessarily an expert magician.
As far as I can tell, there are three main stages in the development of the word "wizard".
If there were a specific word for a trainee sorcerer, I would expect to find it widely used in the annals of fantasy fiction, and I have not encountered any such word there.