Looks like an adult molting into basic (winter) plumage. Juveniles don't have black bellies and some of the feathers show lots of wear (e.g. the tertials which are hanging over the primaries) unlike the fresh feathers that juveniles have. BBPL can also be aged by the barring on the outer rectrix (tail feathers); not quite clear in the image but appears barred as in adult.
As to the sex, well if I had to guess I'd go for female. One can tell the sexes apart by plumage a bit more reliably while they are breeding but I doubt you can during molt or winter.