Lucy is the Princess of all magic, her mother is Layla Dreyar, her father is Zeref Dragonia, and her grandfather is Acnolgia,
At the age of 3 she started to learn magic spells, at the age of 10 she master all the magics and lost magics, Her mother gave her all keys and fuse all and turn into a beautiful staff
Then at the age of 15 she decides that she want to know more about earth and want to go on earth and travel, but her parent disagreed by it, she protested that she wanted to,
So Layla and Zeref made a condition, they will seal her magic and memory for twelve years, and she can freely go to earth whenever she wanted to.
Lucy Agreed, and layla took the staff and separates the gold key , she gave her the gold keys and send her to earth