I have always been curious about this. You will rather frequently see a thread from someone just beginning to play an instrument in which they ask the question "How long does it take to get good". The post is often met with multiple replies that all basically boil down to some version of "it depends". We all know that "it depends" is the correct answer, but I am not sure it is usually very helpful. With all that being said I would like to ask the question in a different way. How long did it take you to get good? How long was it from when you first started playing an instrument until you were regularly playing with others? How long until you joined your first band or music group? How long until you played your first gig? How long until you felt like you were competent or at least felt comfortable referring to yourself as a bass player or (insert instrument) player, or musician?
To get things started I have been playing bass for a little over 3 years. I joined my first band about 4 months after I started playing. It was a rock originals/cover band that was apparently very desperate for a bass player. Three bands later I played my first real gig one year and three months after I started playing. After two years I began to feel comfortable referring to myself as a bass player and musician. I still do not feel like I am very good, but I get better every day.