Here is the info from the WHO guidelines. Sterlizing is to me two different things. I didn't sterilise dummies, water sippies, teethers once my LOs were putting stuff in their mouths from all over the place. No point. A good clean in hot water sufficed.
The issue is formula is not a sterile product. While the risk may be small it is a risk none the less so bottles etc used with formula should be sterilised. As far as I read the risk does not lessen with age. The recommendations are for use with formula not age groups IYSWIM as it remains unsterile regardless of age. http://www.who.int/foodsafety/publications/micro/pif2007/en/index.html
PIF is not a sterile product and may be contaminated with pathogens that can cause serious illness. Correct preparation and handling reduces the risk of illness.
Where available, commercially sterile ready-to-feed liquid infant formula should be used for infants at greatest risk.
PIF is not a sterile product and can pose a risk to infants, particularly if it is prepared and handled inappropriately. Reconstituted PIF provides an ideal environment for the growth of harmful bacteria. Even if present in powdered formula at very low levels, inappropriate preparation and handling of feeds provides ideal conditions for the growth of harmful bacteria, which greatly increases the risk of infection. However, the risk can be reduced if feeds are prepared and handled correctly.
The recommendations below outline the best practice for the safe preparation, storage and handling of PIF in the home in order to reduce the risk of infection with E. sakazakii. These recommendations are also appropriate for reducing the risk of infection with Salmonella.
It is recommended healthcare professionals ensure that parents and caregivers are instructed in the safe preparation, storage and handling of PIF.
3.1.1 Cleaning and sterilizing feeding and preparation equipment
It is very important that all equipment used for feeding infants and for preparing feeds has been thoroughly cleaned and sterilized before use.
1. Hands should always be washed thoroughly with soap and water before cleaning and sterilizing feeding and preparation equipment (as described below).
2. Cleaning: wash feeding and preparation equipment (e.g. cups, bottles, teats and spoons) thoroughly in hot soapy water. Where feeding bottles are used, clean bottle and teat brushes should be used to scrub inside and outside of bottles and teats to ensure that all remaining feed is removed.
3. After washing the feeding and preparation equipment, rinse thoroughly in safe water.
4. Sterilizing: if using a commercial home sterilizer (e.g. electric or microwave steam sterilizer, or chemical sterilizer), follow manufacturer's instructions. Feeding and preparation equipment can also be sterilized by boiling:
a. fill a large pan with water and completely submerge all washed feeding and preparation equipment, ensuring there are no trapped air bubbles;
b. cover the pan with a lid and bring to a rolling boil, making sure the pan does not boil dry; and
c. keep the pan covered until the feeding and preparation equipment is needed.
5. Hands should be washed thoroughly with soap and water before removing feeding and preparation equipment from a sterilizer or pan. The use of sterilized kitchen tongs for handling sterilized feeding and preparation equipment is recommended.
6. To prevent recontamination, it is best to remove feeding and preparation equipment just before it is to be used. If equipment is removed from the sterilizer and not used immediately, it should be covered and stored in a clean place. Feeding bottles can be fully assembled to prevent the inside of the sterilized bottle and the inside and outside of the teat from becoming contaminated.