Really? Some US soldiers in Iraq looked very young, maybe 20? How many years of training can you get before they deploy you, maybe two? Most professions require more training.
Not policework in the US, though: From what Google tells me, training often lasts less than 6 months. In comparison, in Germany it's normally 30 months, but it can vary from state to state (in a few, it's 24 or 36 months).