He does not say how much of your youth you should devote to preaching about the Kingdom. But Jesus did give us the helpful principle to seek the Kingdom first.
لَقَدْ أَكْرَمَنَا يَهْوَهُ بِمَنْحِنَا حُرِّيَّةَ ٱلِٱخْتِيَارِ .‏