How often do you change baby milk bottle?

Is it necessary to change baby milk bottle? i have 12 bottles since newborn. My LO 11months now. I just started replacing some yellowish & the prints coming out.

I change it only when it starts turning yellow. That is because heis 4 years old now. When he was younger id change it every 3 months

i changed them every 6 months regardless how old they are

Every 6 months. But if u are using glass bottle no need

Almost every 6 months

Every 3 months :)

Every 3 months