I do suppose no one truly ever finishes growing up and has that complete knowledge of life. Maybe that's where wisdom comes in. I know some very wise people, but every now and then they don't act so "grown up". And I'm not talking about maturity. I've met some immature "adults" and some very mature "children". I think it's a mix of trying to grow and progress, and to come to a knowledge of truth.
At least for myself, I feel that's what growing up means. Not just simply maturing but coming to truth and accepting things for how they are and learning from it.