My son was around 4 months old, but he's always been VERY independent and had an obsession with doing things that his uncles could do. He's just over 2 now, but I remember him crying and crying at the dinner table when he was 4 months old and wouldn't stop until I put him on the table by the pan of spaghettii sauce and he reached over, grabbed the serving spoon and sucked it clean and dipped it again (first food and he gave it to himself). He's been feeding himself ever since. It's just gotten less and less messy.
Point being, it really depends on the child but they can start pretty early. If they don't though, its nothing to be worried about. They all develop at their own speed.