Yeah, out of the 22 million, how many are fit for military service? Half the population is female, and we can safely assume that 99% of them wouldn't get involved in such a conflict, because honor and all that bullshit; That leaves 11 million, a third of this is underaged children, and a third are old men who can barely put up a fight, let alone pick up a gun, so that leaves 3.6 million. Now subtract those that are unfit for military duty, and those that would switch sides, because they don't like Assad, and you have a very small percentage that puts up a fight.
Also, you can't fight a conventional war with G-3s and M-16s, you need heavy equipment.