Did the randy youth of the those times say, "methinks the lady has nice hamms!"

Well, the sentence you've constructed is more (late) Middle English. And I'm not sure if any youth would be seeing a "lady's" thighs.

In my OE dictionary, ham is glossed as "the ham, the inner or hind part of the knee" and was used to translate the Latin poples (poplitis) 'hollow of the knee'. Here's an old English sentence fragment cited in that dictionary: "Monegum men gescrincaþ his fét up to the ham ... gebeðe ða hamma" (with many a man the feet shrink up to the ham ... warm the hams); writing about some disease, from the Liber Medicinalis in the Leechdoms 1, 26. Also, "mid hommen iuolden" (with bent knees).