Muller was Born September 13th 1989
so unless my maths is wrong he would have been 20 on 13th September 2009
Prior to that he had played the following
2008/2009 season
1 cl game as a sub (18 mins)
4 BL subs appearances (29 mins in total)
at the start of the 2009 season (before he turned 20)he played the following
1 full game (90 mins)
4 subs appearences (114 mins)
so
@Lentwood theory of needing to be a regular by 18/19 in a top league would discount Muller unless 1 start plus 8 subs appearances in the leauge qualifies him as a regular(about 250 mins first team football)?
As you say Lentwoods theory is clearly disprove by many players - but it would be hard to call Muller brilliant with only around 250 mins of first team football under his belt by that point.
Forgive the german spellings but this is the games he played for Bayern prior to turning 20
08/09
Hamburg (11 Mins)
Arm Bielefield (1 Min)
Borussia Monchengladbach (12 mins)
Energie Cottbus (5 mins)
Sporting Lisbon (18 mins)
09/10
Hoffenheim (17 mins)
Werder Bremen (12 mins)
Mainz (57 mins)
Wolfsberg (90 mins)
Dortmund (45 mins)
All stats from Transfer Markt