We started at 5.5 months with DS because he was pulling food off our plates, opening his mouth when you put food up to your mouth to eat, screaming when we would eat because he wanted it. He could sit upright well and wanted to eat. We started DD at 4.5 months on MCHN advice because she was tiny. Doesn't make sense now looking back. I say wait until bub shows signs of readiness. Because Dd was 4.5 months she started on mash and when we moved to finger foods she used to gag a lot. I have found with DS he has been amazing with his food, he doesn't gag and chews well because he has always been in control of when and what he eats.