D.W.
I started giving my exclusively breastfed baby a sippy right around 6 months. I would give it to her with the spout out so she could begin to understand what that thing was I gave to her lol. I just put a tiny amount in because she was going to make a mess with it but it really didn't take her too long to get it. Once I knew she had an idea of what it was for then I put the spout back in. My daughter barely knew what a bottle was.
I have a friend that bottle feeds and she has her kids off the bottle and exclusively using the sippy cup by 9 months old. No bottle fights in her house.