Most players that debut aren't starting material though. Utility guys making their debut at any age doesn't really matter much. They aren't starters. Look at the current Reds starters and when they debuted:
Votto - 23
Phillips - 21
Frazier - 25
Cozart - 25 (only a month shy of being 26)
Mesoraco - 23
Choo - 22
Bruce - 21
Two guys debuted after age 23 and they are the two guys who catch the most flack on the team (from the starters). It is pretty similar around the league. Most guys are in the Majors by 23-24 if they are going to be long term starters.