Depends on several factors: whether you have a natural flair, how much effort you put into practicing, the genre you want to play, level the proficiency you are aiming for, whether you have a teacher, whether your teacher is helpful etc.
You shouldn't be focusing on "how long it will take". If you have an interest, focus on your interest rather than the "end result". That will make it more of an enjoyment rather than completing a task. After all, we all play music for the enjoyment and the fun of it.