The 50-year-old actor believes the 27-year-old screen beauty, who he fell for on the set of 'The Rum Diary', has a lot to teach him about life and insists she's often the one "inspiring" and educating him, despite him being 23 years her senior.
Asked whether the age difference is ever a problem, he replied: "I don't think so. I've got a lot of life experience, certainly, but I don't feel like I'm looking down on her. Or being her mentor. I actually feel like she's the one inspiring me!"
Johnny - who separated from long-term partner Vanessa Paradis, the mother of his children Lily-Rose, 14, and Jack, 11, in the summer of 2012 - also explained why he now feels ready to walk down the aisle with Amber, claiming he never felt ready for marriage until now.
Discussing his reluctance to wed Vanessa, he told Télé 2 Semaines magazine: "Sometimes, even things that seem simple and obvious are scary. I think age, experience and wisdom give us the capacity to move beyond certain stages we didn't dare cross before."
The 'Transcendence' actor also revealed he would jump at the chance to return to his hedonistic youthful antics if he was told he only had a few weeks left to live.
He joked: "I would party every day with all the people I love. I would also take all the substances possible and imaginable ... I would even try and drink bleach!"