It's a very relative thing.
What do you mean by "start talking"? Is saying one word talking? Meaningful communication by a single word? Two or three words strung together? Full sentences? I think for most of us, it's going to be a multi-year process.
In any case, I don't actually know when I started talking, but I'm going to answer at age two, which is probably accurate by one of the definitions I listed above.
I also had speech therapy in elementary school, which I think I finished by grade 3 at age 9.
What I meant by starting talking was the beginning of learning to talk. No one could understand what I was saying when I started.