Why is age requirement different for LASD and LAPD?

Howcome you can be an LASD deputy at age 19 1/2 and for LAPD you have to be 20 1/2?
Update: I read on the LASD recruitment website you have to be 19 1/2. On the show "The Academy" there were recruits in the academy that were only 20 years old.
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