For some reason people go bonkers about waiting til 6 months.
NICE guidelines say the best thing for a baby is to be exclusively breastfed for 6m. Most people don't don this, but bottlefeed, which is not necessarily better. And because their babies get hungry they give them that stage 2 hungry milk, which is definitely no better than giving solids.
My hv said that they discovered that in parts of the world where weaning was delayed til 6months there were fewer allergies. BUT these also happened to be mainly the developing world, so lack of allergies is probably due to a better immune system.
Clearly weaning at 4 months does no harm to most babies (as we all survived to adulthood and were weaned at 3 or 4 months as that was the advice 20-30 years ago). Also, my dd was premature and we were advised to wean earlier than 6 months as it is important for them to have the extra calories.
You need to watch your own baby to decide what they need. I think it's quite cruel when people insist on hanging on til 6 months while poor starving baby chews his arm off. But if your baby is doing ok then you can wait.
I personally prefer to wean earlier so you can do it slowly and they can learn to take food from a spoon in their own time rather than needing to do it for nutrition. By 7 months babies are supposed to be on 3 meals a day, and this seems like a lot of work to do with them in 1 month.
But be prepared that it seems to be one of the rules of mumsnet that you never wean a baby before 6 months, hence the angry mob with pitchforks.