The logic from my doc and dentist is that the sugar in milk erodes their teeth which is why we brush before bed
I've been told they should be off the bottle by 15 months because it can cause cavities. Bottles and sippy cups also require a different mouth shape than open cups or straw cups, so doctors are generally recommending against sippy cups and suggesting going right to straws now. Mine has been off the bottle since January and has only used a straw cup.
Son is 16 mo old. We give milk bottle in morning when he wakes and an afternoon bottle. After bath and teeth brushing at night he only gets water