meantolearn“Is 'born to live' an idiom?”
No, an idiom is an expression that by convention means something different than what would be expected from a literal translation.
Example: 'John kicked the bucket' sounds like he simply walked over and struck a pail with his foot. However, by convention it means that he died.
meantolearn“What does it mean?”
I wouldn't even call it a common expression. There is the expression 'live the life that you were born to live'. Which means be who you are; be true to yourself.