A grown-up relationship is a relationship where you are individual people allowing each other to pursue your individual goals and support each other in those goals while having an overarching similar goal in life. It's allowing each other to be individuals and grow in your own things together. It's about being supportive and individualistic. It's balance. It's really all about balance.
I agree I think that you can grow together but separately because you are two unique individuals with different interests and talents and things that you want to work on and if you find joy in something that your partner doesn't I think it's important that they appreciate that you find joy in that and support you in that and vice versa