Once for all, I have sworn by my holiness- and I will not lie to David- that his line will continue forever and his throne endure before me like the sun; it will be established forever like the moon, the faithful witness in the sky."
Psalms 89:35-37 NIV
God has declared David to become a king and will reign forever. I believe that's His vision for him. David is still young when God used him but because it is aligned with God's plan, it happened. Same goes to us, when God has spoken to us, it will soon happen. It will be established. It's not a matter of 'Will it come?' but 'When will it come?". Declare it with conviction. It might be financially, physically or spiritually, when God gives you vision, it will happen. Our trust has a great impact so keep trusting God.
Even if we cannot see it happening now, God will let us see it soon. And when we come to the time when we think it's out of our control, He is still in control and forever will be.