Guidelines are usually to wait until LO is 6 months old before starting solids, although of course some do start earlier for various reasons. Personally I would not start as young as 4 months unless there was a medical reason to and discussed with a paediatrician.
From 6 months are are few foods baby shouldn't have really.
I started my DS at 5.5 months old and used BLW, so finger foods only, no puree at all unless it was something like humus which is a purée anyway. Started eggs, meat and fish and all sorts of foods. At 6 months he was chomping on a slab of roast beef in a restaurant and thoroughly enjoying it - big enough for him to hold in a fist grip and gum and suck at. He was always an enthusiastic eater so tried pretty much everything he was offered. As time went on he showed he wasn't a huge fan of meat although he's always had an unbelievable appetite for slow cooked lamb shank.
