"I've heard people say that too much of anything is not good for you, baby."
Barry White, too much of anything is indeed not good for you.
In the NBA, teams love to have youth. After all, it gives hope for the future. But, too much youth can be so catastrophic to the present that you don't live to see tomorrow. An immature player like Stephon Marbury can run amok and never really learn how to be successful in the league.
Moving too far in the other direction, however, makes a team experienced and wise, but perhaps too old and slow to compete. The key is to always find the right balance of youthful progress and veteran know-how.
Some NBA teams have definitely put together youthful cores that do promise that brighter tomorrow, but only if they can find sage veteran leadership in time. Having veterans gives the young players someone to learn from, someone who can shoulder and deflect criticism, someone who has "been there before" and isn't rattled during pressure moments.
Plenty of NBA teams actually have veteran leadership; they just don't have the younger talent to make the formula work. However, the following teams have all found their core of youth, but desperately need more experienced NBA players to balance their roster.