My life experience has generally found this to be true, BUT a young person can suddenly have an epiphany and still reach their potential.
Young players who have recently become dads are one example (can't wait to see where the thread goes from HERE!)
I've been coaching youth soccer for 6 years. Some of the best players I've had, had to be motivated repeatedly. Its frustrating, and if it gains momentum it can bring the team down. I really thought Joey was dialed in down the stretch. Thats a good sign, that the playoff run got him fired up, now he has to find consistency for a full season of play. He's not unlike some of the kids in EDM and COL in that respect. I like how JK and Todd handled it, send him down to correct the attitude. A strong locker room will help too.
As for children. Well, it made a bigger difference in my life and career than I can measure. Its huge. Maturity can come from other events in your life as well.