Regulation soccer games are made up of two 45 minute halves. The referee officially keeps the time, though in High School and College soccer, time may be kept by a game clock. In professional soccer the referee keeps accurate time and may add additional time for stoppages such as injury. In professional soccer there is actually a fourth official who keeps things off the field organized but can also step in if one of the three other officials are injured or cannot finish for some reason.
In youth soccer, the length of the game is less with the lower divisions. U6 and U8 in USYSA are divided into four quarters. This is to give coaches a break in the game to explain things to the younger players.
U6 is divided into four eight minute quarters, for a total game time of 32 minutes.
U8 is divided into four 12 minute quarters (total 48 mintes).
U10 is divided into two 25 minute halves (total 50 minutes).
U14 is divided into two 30 minute halves (total 60 minutes).
U16 is divided into two 35 minute halves (total 70 minutes).
U18/19 is divided into two 45 minute halves (total 90 minutes)