Single for a Reason

Lately I've been wondering, is it awful to be 35 and single? Or to be more specific, is it awful to be 35, FEMALE and single? Are women in their mid-30's single for a reason? I would like to think that my excuse is that I was career-driven and just had not met the right guy. For some reason that seems to be a perfectly plausible and even admirable response for why a guy is single, but why are our standards different for women?