How to politely tell friends and family I don't want their advice?

I have a baby who will be 5 months old on the 10th. She is growing and thriving just fine on milk, however many of the people around me try to give me advice especially with what they think she should be eating I had a friend try to stick a carrot stick in her toothless mouth because " I should let her taste things to see if she likes them" but the one that bothers me the most is my grandmother she's 80 years old and has been begging and pestering me to give her cereal since she was between 8 weeks and 12 weeks old. I don't want to hurt my grandmother's feelings but I think I did this morning, she said "it's just that maybe she won't be so attached to you if you start feeding her" but that's the point of doing it, the bond and the baby is not quite a supported sitter yet, I know medical advice changes and her kids all turned out fine, but this is my baby, and I don't think she is ready for it.