Typically, babies may be able to start really talking around 10 months of age. By really talking I mean the ability to say words that are audible enough for any one to understand. Babbling can occur earlier then 10 months, but generally sounds like the baby's attempt to copy the people around them. I do know of a baby being able to talk as early as 3 months old. That however is very unusual.
I wouldn't really give a set time, because you'd be surprised if we say 10 months and your child talks at 6. It depends how their body develops and how much they are exposed to. My son talks, not in complete sentences, but enough to get his point across, and he is only one but started the majority of his words at 9 months.