It differs for many kids.
Some are just lazy, like my ds, and I held his bottle until we tried to get rid of it around a year! :shock:
But, it also helps with the bonding, in my opinion.
Have you tried to get your lo to hold it and she just doesn't, or holds it for awhile and throws it? :wink:
It IS nice though when they start - just one less thing you have to do! :wink: