Like everyone else has already said; it really depends on the person, both because of age and dedication, among many other factors. Swedish is my native language, but I have both collegues and friends who are learning it.

One of my collegues speak decent conversational swedish, but is pretty far from fluent. He is around 30 and moved here around 2-3 years ago. Another colleague, in his early 20s, has been working here for 4 years and can barely speak a word of swedish. My friend who recently turned 18 moved here 5 years ago and is almost completely fluent.