When and how to transition to sippy cup?

A❤️C

I read online you can start at 6 months but when I mentioned it to my sons doctor at 6 months he looked at me like I was crazy...

My son is almost 8 months now. He is bottlefed. When and how did you start the transition to a sippy cup? I wanted to start earlier than 12 mouths because I think it would be easier to do it earlier before they build a strong attachment.

Any advice appreciated :)