I just looked into the Kroos example myself and realized even then it doesn't bode well for the argument.
He played for Bayern Munich 2, so they had a B team, then was promoted to first team at 17. Which sounds great... but he played 19 games over 1.5 seasons, not great, then got loaned to Leverkusen for 1.5 seasons. So even Toni Kroos had to go on loan.
Kroos came back to Bayern and became a regular at 20 years of age.
Similar kind of situation with Philipp Lahm, he went on loan for 2 years then came back to be a starter at 23 years of age. The whole loan thing isn't as uncommon as people perceive.
It just was not clear for me with that data. Lahm was on loan - but with a club that played in European competitions and he was a permanent starter for them, playing e.g. two full matches against CR7 and United in his first year. He got his first caps in that year, too, and from then on had his place in the German national team before returning to Bayern. Similar story with Kroos - he got caps before he returned. You count Khedira's first European years at Stuttgart - but not Lahm's...
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I am not obsessed with getting the young ones to play too soon. But Klose has given a good interview today about him and Müller. Both were fighting against each other in the 2009/10 for the same position as Klose was used as a 10 then and not as a 9. He said that Müller earned his spot in that year against him. Van Gaal gave him the chance - but he took it with full hands and performed like this the whole season - was Bayern's best scorer in that season.
But it makes you looking at the situation of Hummels, Badstuber, Müller and Kroos - all from the Bayern academy. They are born in a period of 13 months with Hummels born in December 88, Kroos in January 90. Kroos and Hummels were brought into the squad with 17 - did not play much and saw the bench a lot - were then loaned. Badstuber and Müller finished school or made their civil duty year (instead of military) and then spearheaded the Bayern reserves in the 3rd league. All of them had their first real season in 09/10 and whereas Badstuber and Müller were starters in the World Cup, Kroos only was a substitute and Hummels was not invited.
Young ones need to play for their development. On a level they can cope with and grow. Not too big that they sit on the bench - that is a waste of time - but not too low either. Müller and Badstuber have learned a lot in that 3rd league team that was just midtable then but in which they were leading players and carried responsibility. Müller had the mentality and the help of a van Bommel who took care of him off the pitch in the first year at Bayern. Andries Jonker, van Gaal's assistant (later head of Arsenal's youth academy, right now Wolfsburg coach) told that Müller came to him in every halftime and after the match to get advise - like he got the previous year of Gerd Müller when playing for the U-team.
I do not think there is a right moment for every player - you have to look at every player separately what is best for them now. And a lot can go wrong. But if they do not get chances they cannot go nowhere. Getting loaned to clubs that do not play them does not help either - if it is not the EPL there is other countries where they might have the level and the clubs the guts to use them. They have to be in the competition for the spots - they should not play just because they are kids but if you put them into the squad you have to give them enough time to play in the easier matches (not all at one time but the older ones should be able to carry a younger one).
All of the big clubs have the same problem - the gap between academy and club level is too big. In difference to the last seasons since Alaba we have some really promising youngsters right now that really seem to be able to make it - atleast one or two of them should do it. You can see atleast that they should be able to make it Bundesliga level - that rest time will tell. That will get interesting.
