How old was your baby when u started giving them food?

my son didnt start till he was 7 months old. my daughter is nearly 5 months old and is startin on food. my health visitor says you shouldnt start them on food cos it can cause obesity, wot a load of codswollop. mom says i was started on food when i was 5 months old and i may have been chubby when i was a kid but i grew up to be slim. where do they get these facts from to say early weaning can later cause obesity?