A baby should ideally be weaned off the bottle before age 1 year old and then transition to a sippy cup.
But if the 2 year old will not use a sippy cup and only drink milk from the bottle then there's nothing wrong with that.
The bottle is just a drinking device and as long as the 2 year old is getting the fluids and milk he or she needs then that's really all that matters.
If you haven't introduced your 2 year old to a sippy cup then now would be the time to do so and they make sippy cups which has the feel of a baby bottles nipple to help make the transition easier.
Once they get the hang of drinking from a sippy cup then you can transition the child to regular cups.
Most babies are ready to get off the baby bottle and transition to drinking from sippy cups by age 6 to 9 months of age.
And then by 12 months they are usually ready to ditch the bottle all together and by age 14 months or so they may be ready to drink out of a regular cup.
But if not just keep them drinking from a sippy cup to avoid spills.