Ditto what kickball said (got to K and skip 1st). Our experience has been that it's not a state mandate but an individual district policy. Our district did require testing, and the tests had to show an age equivalency of 7.
We did early entrance into first, and we're not entirely sure it was the right move for a couple of reasons. The curriculum still doesn't match DS's needs and for the first half of the year the all day schooling was very, very hard on him. Now our kid does need a lot of sleep, so take it for what its worth. But we did underestimate the effect of being in school for a full day. Looking back on it, we might have done better for DS letting him go to half-day K and then doing more afterschool learning.
My two cents.
JB