6 months. I bough Nestle cereal. Add milk powder. At 8 months u can add flavours like carrot/veggie (Nestle sells that). At 10 monthes u can add some meat. My son hated Gerber.
Why trying new food. Day 1, give one spoon. Wait to see if there is any reaction. If all is fine, add another spoon the next day, until it can eat a small bowl.