Some solids are fine to offer to a baby at four months of age, some babies need and want the extra nutrition, every baby is different.
not wanting to start a debate:P but at that age solids are not going to give them much nutrition wise, its mainly to teach them how to eat a tiny amount - and it has been proven that you increase the risk of your child having (possibly serious) allergies if you start solids before their gut's/immune system is old enough to cope, which is around 6 months roughly for all babies. sure every baby is "different", but please dont spread around your opinion on information that is not medically researched and backed up!