I think it's interesting how he said he wanted "a very attractive woman", rather than "a fit and healthy woman". To me, that suggests that he is looking for the type of narrowly defined beauty that society today deems is the 'in' look.
For example, if he met a lady who exercised regularly and was very healthy, but had a plain face, glasses and frizzy hair, would he want to date her? Judging from the tone of his letter, I doubt it.
At any rate, I don't know what he was hoping to achieve with his letter. Did he really think Abby would agree with him, and exhort all her female readers to pay heed?