Usually, the recommended is 6 mths. 4.5 mths would be the age where my mum or mother in law would ask me to start weaning. Some kids dont't face any problems when weaning that early. But as a general rule, you should observe if your baby is ready to be weaned at 4.5 mths.
Your baby should be able to support her head with her neck properly and somewhat sit to ensure that she doesn't choke on food.