Is there any word which describes a person who is inexperienced but has the potential to become something in future.
Define what skills/abilities provide the "potential" and you may find the answer you are looking for.
To me the word capable sums it up. --you possess the competence and ability. You dont have to be proficient to be capable.
I own a Concrete Construction company - We often hire or recruit just this type of person. In most cases they are "green" (inexperienced, untrained, new to the trade)
We call greenhorns who display early talent an FRP (First Round Pick), prospect, or joke that we need to give him more "PT" (Playing time)
Trade specific Our shop hands often lack experience with certain equipment but are "Mechanically inclined", also referred to as a wrench or gearhead. "He hasnt worked on equipment this size but the kid is a gearhead"
Phrases we commonly use for laborers: He's green, but fits the mold or has the mindset - has an eye for it - shows the signs -has the mentality or work ethic
For the ones with a brain: Wont take him much effort to climb this ladder. He's old for his youth. - sees the big picture
Is there any word which describes about a person who is inexperienced but having potential to become something big in future?
The word is Potential but you already used that in your question.
potential noun (ABILITY) someone's or something's ability to develop, achieve, or succeed:
Example [ + to infinitive ] You have the potential to reach the top of your profession.