My reason why I ship Elsa from Frozen and Jack Frost from Rise of the Guardians, is that both were meant to be together.
Because it's a Romeo & Juliet style romance. Elsa and Jack are in a forbidden love and they love each other.
Many would say Jack is young like 18 years old and Elsa is old like 21 years old. But news flash, Jack Frost was ahead of Elsa because he was born before Elsa thus making Jack older then Elsa. Jack Frost is an immortal while the beautiful Queen Elsa is mortal.
My why I like this ship is because these two frozen lovebirds should be a couple because both are quite similar except the gender.
Both have powers of ice and snow. Both are very unique people. And both are very young.
That's my reason.