It’s best to continue sterilising your baby’s bottles until baby is atleast a year old because they are vulnerable to the germs. These germs can develop very easily in leftover milk especially those that might be collected in bottles unknowingly. Sterilising is the only way to make sure baby's bottles are free from harmful bacteria. If baby is old enough, sippy cups or beakers might be better for your baby's teeth than bottles. They also don't need to be sterilised, because they're easier to clean.
For me personally, I stopped sterilizing his bottle when he started on solids. Reason is because my son has already started stuffing everything in sight into his mouth, and it's also impossible for me to sterilize his food all the time. I didn't want to too "protective" against germs so that he can build on his immunity better.
thanks