Hi Paul yes I agree that it should start right away, but alas that's not always the case for Paul sates
For when for the time ye ought to be teachers, ye have need that one teach you again which be the first principles of the oracles of God; and are become such as have need of milk, and not of strong meat. 13For every one that useth milk is unskilful in the word of righteousness: for he is a babe. 14But strong meat belongeth to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil.
1Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God, 2Of the doctrine of baptisms, and of laying on of hands, and of resurrection of the dead, and of eternal judgment. 3And this will we do, if God permit
Paul is does not say they are not saved who only drink the milk, but he encourages those who still drink milk to go on to perfection. And that is what we are to do also for babes in Christ.
This is brought out more forcefully when we read what Paul said here
1And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, even as unto babes in Christ. 2I have fed you with milk, and not with meat: for hitherto ye were not able to bear it, neither yet now are ye able. 3For ye are yet carnal: for whereas there is among you envying, and strife, and divisions, are ye not carnal, and walk as men? 4For while one saith, I am of Paul; and another, I am of Apollos; are ye not carnal?
Paul still called these babes his brethren even though he knew that they were still not able to eat meat. Babes are saved but have need of teaching that they might grow some teeth and be then able to eat the meat. There is a growing process in Christ no one starts as an adult.