This is the way of society, this is why you won't hear any guy's new girlfriend going on about her slutty past, women do well in covering that up, doubt any guy would really want to know. Any guy thinking the woman they are newly dating is some innocent virgin though has to be very naive, likely a lot of women of today are hitting those double digits.
I don't want to judge people and I see were you are coming from OP but you aren't going to stop anyone judging others, just focus on yourself and how you conduct yourself that's the best you can do and hope that it reflects well on others in how they choose to behave.
I must add I find women can be as sexist as men in other departments so let's not point the finger at the male sex.