Obviously experience comes with age how can you expect younger players to come at level of Ronaldo, he is the king and he'll ever be because of his experience age and game .
No one can replace him for a long time in football world but yes many good footballers came into light during fifa world cup and In next world cup they'll be polished more and they'll show more good performances.
There is no need to think like that about a player even if that player is Ronaldo and he achieved many titles, A few years ago when we had stars like Ronaldinho we were thinking there will no player with high performance like him and he should play for his team even is he is old but not brazil got Neymar who is a superstar player for his national team, it will take some time but in the end, the young player should have the chance to show a better performance.