He got a few games at ages 20 and 21 but became more of a regular at 22 when he appeared in 69 games--not a huge difference agewise. The argument was that the Twins don't play guys at the MLB level at that age, which doesn't ring true. Mauer debuted at age 20, Torii Hunter at 21-22, Cuddyer, Kyle Lohse, Matt Garza, Morneau, Sano, Kepler, and Arraez all made their first appearances at 22. Again, the original post was referring to 20-21 year olds, but I'd argue there's not much of a difference playing a 21 year old and a 22 year old. Point being, the Twins don't avoid calling guys up at that point because they're young. It's because there aren't too many guys demonstrating that they're MLB caliber players in their early 20s. I'm guessing the Twins aren't abnormal in their decisions to play guys real young. ETA: Stay and star at the MLB level are two very different things, ones that most MLB players never achieve no matter their age.