I don't see it as an old man's name, but i'm biased because i have a 3 year old nephew called
Calvin, he goes by
Cal alot of the time and although i wasn't sure when they first named him, now i think it's really well suited to him, and works fine on children.
If she really doesn't like it though then surely using it as middle name is a nice compromise, though i'm not sure it would work as middle name for either
Christian or
Dylan