I think the best way to tell is see how he physically compares to a mature doe, if you can catch the two of them side by side. If the spike is smaller than the doe you definitely need to let him walk, as he's too young. If he is as large as the doe or bigger then you need to compare him to a young buck like a 6-pointer or so and see how he compares. That might help make your decision a little easier. I live in an AR county too, but some of the spikes I let walk last year appear to be turning into nice little bucks so far.
AF(Retired)/DV; busted mine to save yours then...bustin' Bambi to save the American hunting dream now!