sip cup at 7 months ?

Linda
My daughter is 7 months and got teeth on bottom , my doctor said recommended 9 months go from bottle to sippie cup since easier then waiting till 12 months . This is my 3rd child my next to oldest is 9 so i don't remember if i gave to him 8 th or 9 th month i will see how everything goes next month before trying that. What all think ?