i am glad to see that you are back :-)

I think that the usage of B and S words to name an old maiden and an unmarried man is purely accidental. I compare it with a totally unrelated language (Russian, as you probably guessed) and here a spinster is called literally "old virgin" and a bachelor has the same root as the verb meaning "to be neutered". I know that Russian women used to do a lot of spinning as well but still we do not call an old maiden "prjadil'schica"