My baby is now 18 months, when can I stop sterilizing her feeding bottles?

I stopped sterilizing my son's bottles when he started his solids. His food isn't sterilized, and so is his powdered milk. It doesn't make any sense to sterilize the Avent Steamer & bowls each time before use and my son was already stuffing everything in sight into his mouth. Plus, I am one of those parents that don't believe in protecting my kids totally against germs and bacteria. My cousin is very particular about hygiene and cleaniless with her daughter but she is still falling sick much more frequently than my own daughte. (They attend the same child care).