Can you start solids at 4 months?

Just curious because I heard one girl did that and I was just super surprised. I wouldn’t ever take that risk because I’m super careful kind of person but let’s say a baby is already meeting all the qualifications needed at 4 months can you start the solids? I know her baby was pretty big at birth so I’m sure she started that early because her baby probably was already sitting up and etc. just curious about it.