Hi
smithclarkson01this is highly subjective. English proficiency, academic background, working culture, and wealth widely varies.
Natives have some advantage over non-natives.
Also non-natives widely varies. Some countries have high English proficiency index while others have too low proficiency.
The academic background is a significant factor. Business and engineering backgrounds are supportive.
The experience in an English working place is also an advantage.
Some students are self taught because they can't afford taught courses by experts. Some students even don't have the luxury to pay for the exam more than once.
some students may require only 2 months while others may need a year to reach 700+.