We’ve been on size 3 since maybe 4 or 5 months, can’t remember exactly, but definitely had been on it for ages by the time they reach 9 months.
I breastfeed and use a size 2 teat
Mine on size 1 at 8 months. It's advised if you want to breast feed alongsixe to stick to a slow flow. So 0 or 1 because a fast flow from 2 and above is usually faster than a breast flows and thus will get bottle preference over breast. So it depends what you want.
My 10 month boy is happy with 2, 3 he ate too fast and often sicked up xx