The book "Hey, God, Why Is It Taking So Long? by Lynette Hagin was extremely helpful to my personal situation. I was a late bloomer in discovering my service and my purpose for God, so at times I felt as if I had "missed the boat" so to speak with God.
However, Lynette's book explained that God works in our lives in steps, guiding us and preparing us for the special work He has given each of us. This is why it's important to remain close to God and remain prayerful. She also explains that just because some of us have let years go by without obeying God's will for our lives, that doesn't mean that it's "all over" for us with God.