Is 5 months too young to introduce sippy cup?

[LostinMI05]

I have a 5 month old that is breast-fed exclusively. I was pumping at work, so he had expressed milk in a bottle while I was away. Now I am at home with him, so he gets straight from the source. But I have one bottle of expressed milk that is going to go bad if I don't use it in the next couple of days. I was thinking of using it to introduce a sippy cup. What has been your experience with introducing cups? Is 5 months too young?
Thanks,
Amber