As a disclaimer, if the family is poor and live in the middle of scenic nowhere, and there is nowhere for the teenagers/young adults to go (my situation), then I can give them a light pass for not leaving the nest at the appropriate age. But if they are every bit capable to succeed within their environment, even if their financial situation isn't the greatest, then there is no excuse for the 30 year old man child issue to persist.
When it comes to seizing positions in jobs and moving up the ranks, it's usually all very political. Having a good relationship with your boss and colleagues is better than not having one at all, but family or close family always trumps all else, for example. Either you're just not good enough (or they don't perceive you to be), or you are in an unfortunate situation where no matter what you do, the boss will always favor their cousin fifteen times removed working alongside you, and eventually, ahead of you.
Another piece of advice I always try to bestow upon people is to keep their dreams within sight, but always have a plan b or a plan c. Sadly, most youth are taught these days that they are special, that they can succeed if they believe hard enough. What foolish lies. Sure, that may be true for the few, but even for them, intelligence, talent, etc. were not the only factors that played in their success. Often times, it was due to simple dumb luck. Most people will end up working as clerics, cashiers, waitresses, you get the drill.
Regarding my situation, living at a dead end street in a dead end down in the middle of nowhere, my only opportunities lie in online work, which I am currently pursuing. If I fail, so be it; they can't all be winners.
My final piece of advice to you is to ignore the wishful thinkers, the unrealistic optimists. The people who have to scratch for every penny (for example), but believe that one day, they will live in their own personal manor, and will not accept any kind of realistic feedback in regards to their pipe dreams.