Not difficult. See individuals and teachers for half a year. Some teachers only teach music, so they may reach Grade 3 or 4 in half a year. If they study well and systematically, they may only reach 1 or level 2 (this is already very fast), because they spend most of their time practicing fingering, hand posture and mastering rhythm and intonation. Personally, I admire the second one, because after such study, most songs can be learned by myself after 3 or 4 years. If you are an adult, it may be slower, because your hands are not as flexible as those who have studied since childhood, and it takes more time.