I really don't know.. I always sang along from when I was a young boy, and I just so happened when I got older, to still enjoy singing. I know that there's voice coaches out there, though. You shouldn't be limiting yourself with time, however, if you truly want to sing.
I kind of just taught myself, maybe took me a few years to become decent. If you're serious about it, then you should take lessons. Teaching yourself can actually be bad in the long run if you end up using the wrong techniques that strain and damage your voice. And not everyone can be taught to sing of course, it has to come at least somewhat naturally. Some people are just tone deaf.
I've been singing for years. I guess I "learned how to sing" at an early age using Guitar Hero (you'd be surprised at how good those games are for teaching you how to pitch a note) but if you were really dedicated, it might take you a few months to get to a decent standard. Are you asking about singing in a band, reading from sheet music or just singing along to the radio?
You shouldn't look at it that way. That's the mark of a quitter. If you are determined to become a good singer, you won't be putting yourself on a timetable.
It probably took at least a year before my range began to increase substantially, my breathing was correct, and my voice was placed properly. But as I said, time isn't important, and you'll go at your own pace. Seeing a vocal coach is very helpful, as well.
You dont ever really stop learning. The older you get the more your voice matures and changes. I started singing as a kid and I sound much different now. If you're really asking how long did it take to improve, about a year or so in my school choir. But I'm always improving and you never stop
I began singing in school choir at 11 years old. I was in public school choir for 8 years. I have always been an alto and I began to be able to sing higher by the age of 17. I took voice lessons in high school too