N the bottle bound to change colour (to yellowish, especially if it's used to store breastmilk). just use until you think the bottle is no longer clean. I dont really go n remember how old is the bottle.
I have friends who use the bottles until 1 year. Baby looks ok too.
Only regret I have is to train baby on tommee bottles. Not that it's not good. But I think pigeon always have those trade in program to exchange new pigeon bottles, I think that is a good deal. Rather than throw away the old bottles.
According to the manufacturers:
Teat to change every 3 months
Bottle to change every 6 months
But it really depends on you.