How long does it take to become fluent at the level of a native speaker?

Has anyone had the experience of beginning to learn another language as an adult who later reached native speaker fluency level? I began studying another language 3.5 years ago, managed to fall into a job about a year ago where I speak that language most of the day and speak it socially most of the time. However, I still struggle with generating some of the verb tenses during conversation and I stumble at times trying to remember the gender of a noun or the order of the words. Some of the most difficult verb tenses I am still unsure about. My vocabulary is broad enough that I had no trouble reading "The DaVinci Code" in translation, but I couldn't make it through a more intellectual text. I am told that my accent is excellent. While I know I continue to make progress every day, I am wondering how long it takes for everything to fall in place.