All pea combs have 3 rows (or at least they should). In males the three rows usually grow much larger, making them more distinctive. In females, it's usually only the middle row that grows larger making it look like she only has one row. The comb in the first picture does have three rows but they all seem to have merged together making it look like one big one.
Thus far all of my AMs have been very slow to mature, though it's not a very large sample pool. I have never had a pullet get any sort of comb growth or reddening until right before she lays, which I want to say has been closer to 24 weeks.
My guess is that this Lav AM is a cockerel.