Then I suggest you read the link I supplied fro Rabbi Singer.
I read it shortly after you posted it. So what? Singer decides to ignore the text, which clearly identifies Agur son of Jakeh as the author of what we call Chapter 30, and claims solomonic authorship for Chapter 30. Wow. OK. He doesn't take the text very seriously, does he.
As far as Singer defining "almah," I don't see him "defining" it. His discussion of vv. 19-20 is interesting, but to me not convincing, because I don't see the requisite relationship between the two verses. In other words, I'm not convinced that the "young girl" of v. 19 is the "adulteress" of v. 20. I just don't see the vital linkage between the two verses. I tend to see the adulteress of v.20 as a contrast to the young girl of v.19 rather than as the same person. Nor do I think that the young girl of v. 19 is necessarily a virgin. It's not clear at all from the text. She might be; she might not be. The adulteress clearly isn't.
Singer is exactly what I've mentioned. He's part of an organization (Outreach Judaism) that is specifically an aggressive response to Christian teaching. I'm not saying that there's anything wrong with that; I'm just saying that the nature of the organization defines how they'll approach certain subjects (as does my identity as a Christian admittedly influence me) and perhaps lessens their credibility by clearly indicating their bias. Outreach Judaism and its supporters will find the best way possible to challenge, question and raise doubts about Christianity from a Jewish perspective. Consider this paragraph:
Rabbi Singer said:
For nearly two millennia the Church has insisted that the Hebrew word almah עַלְמָה can only mean “virgin.” This is a vital position for defenders of Christianity to take because Matthew 1:22-23 translates alma in Isaiah 7:14 as “virgin.” The first Gospel quotes this well known verse to provide the only “Old Testament” proof text for the supposed virgin birth of Jesus. The stakes are high for Christendom. If the Hebrew word alma does not mean a virgin, Matthew crudely misquoted the prophet Isaiah, and both a key tenet of Christianity and the credibility of the first Gospel collapses.
First of all it's clearly not "vital" for defenders of Christianity to insist upon the translation of "almah" as virgin - since I know many Christians (including myself) who quite cheerfully acknowledge that "almah" doesn't literally mean "virgin," even in Isaiah 7:14. It means "young unmarried woman." So where he gets how "vital" this is for defenders of Christianity I'm not sure. The stakes really aren't all that high for Christianity - only for absolute literalists. I don't have any particular problem believing in the virgin birth, but I also don't consider the virgin birth as vital to my personal faith, and if it were ever proven that Mary wasn't a virgin nothing significant of what I believe about Jesus would be challenged. I'll acknowledge that absolute literalists and fundamentalists would take a different approach. Also, Matthew's Gospel doesn't crudely misquote anything. Actually, Matthew quite accurately quotes the Septuagint. Rabbi Singer may not like what the translators of the Septuagint did with Isaiah 7:14, but it was the version of the Scriptures that was in the widest circulation among the Jews of that era. So Matthew doesn't crudely quote anything. He accurately quotes the Septuagint, which Singer may consider a crude translation - but that's not Matthew's fault.