Agreed, gunnarthor, which is why I argue to bring up players faster....so they are productive sooner. There is risk in every approach, I'd rather roll the dice on the faster process, but I realize not everyone agrees.
Well, looking over the last decade or so these players debuted at these ages w/Twins:
20 - Rivas
21 - Ortiz, AJ, Hunter, Guzman, Santana, Adam Johnson, Mauer, Liriano, Casilla,
22 - Milton, Radke, Lohse, Rincon, Cuddy, Morneau, Kubel, Durbin, Crain, Garza, Gomez, Revere, Ramos, Hendriks, Arcia
23 - Mays, Romero, Restovich, Baker, Perkins, Slowey, Benson, Parmelee, Hicks
24 - Dougie Baseball, LeCroy, Jones, Kielty, Bartlett, Boof, Span, Plouffe, Pinto
25 - Koskie, Guerrier, Neshek, Blackburn, Valencia, Waldrop, Swarzak, Gibson
26 - Buchanan, Ford, Duensing
This obviously isn't everyone - no need to look at Morales or Miller but it's a decent list. Not sure age tells us much. Obviously, the better players got up faster, which isn't surprising. (I think everyone except Hendriks and Casilla in the 22 or younger groups had been ranked in the top 100 at some time). I tend to think that the Twins are more willing than other teams to let "old" prospects contribute. (In the 24 and older group only Gibson - who had TJ surgery - was ranked by baseball america, I believe). It looks like the Twins have tended to get the franchise type players and the first division complementary players get their feet wet by 22 and hope to establish them within two years of that.
I guess I'm just not sure that the Twins have been holding elite talent back. I know some people thought Cuddy should've been a regular before 05/06 and injuries held back guys like Kubel and Gibson and some guys struggled after being called up (Hunter, AJ, Johnson).