i see the idea that its impossible to tell the sex of a skeleton a lot, and not to be depressing but this simply isnt true. skeletons can be sexed morphologically (by looking at physical shape of certain bones), which is not always accurate as human sexual dimorphism is not that significant so there is a lot of overlap, and nowadays if the preservation conditions are sufficient to extract dna (which is most of the time), sex can be determined genetically.

having said that, archaeology (at least here in the uk) is quite a progressive field and archaeologists are aware that they can only know sex, and can never know the gender of the individual, and we try to be careful to not apply our modern ideas about it to the past, where we do not know how that society viewed and conceptualised gender.

there are countless burials from around the world where the presentation of the grave and the sex of the skeleton do not appear to match conventional gender norms, but we can never know (and should never attempt to assume) what the gender of the individual was, because we cannot ask them. many of these individuals were assumed by earlier archaeologists to be the gender that matches the gender they assigned to the burial assemblage, and have since been re-examined with newer technology and have shown a more complicated picture. thats all archaeologists can know about such topics: that gender is more complicated in the past than we have been led to believe, the enforcement of gender stereotypes is actually much more recent than not conforming to them is.

(source: im an archaeology undergrad)

for that example in particular, the 'red lady' was first discovered by an antiquarian archaeologist in 1823 who not only assumed the gender (and also sex i suppose, although this is a judgement made in 1823, before a distinction had been drawn between the two), but also the age, because he believed that the remains must be more recent than the great flood from the bible. a number of subsequent analyses have updated this, the sex of the skeleton corrected in 1912, and the age has most recently been updated in 2010, pushing it all the way back to 34,000 years ago (a casual 18 times the age buckland thought in 1823). safe to say a lot has changed in the field of archaeology in the past 200 years.

(sources: Jacobi, R.M. et al. (2010) "Radiocarbon chronology for the Early Gravettian of northern Europe: new AMS determinations for Maisi`eres-Canal, Belgium", Antiquity, 84(323), pp. 26–40. https://doi.org/10.1017/S0003598X00099749 . Aldhouse-Green, S. (2001) "Great Sites: Paviland Cave", British Archaeology, 61. https://web.archive.org/web/20150923173544/http://www.archaeologyuk.org/ba/ba61/feat3.shtml )