Mens sizes have changed over time. Go get a vintage t-shirt from the 80s, medium size, and try it on. It'll be the size of a small or xs today.
I wish! That number is kinda-sorta-related-to inches, but it's not, at least not anymore. I wear a 31 or 32 jean, but my waist is about 34.5 inches. And any jeans which fit my thighs properly (turns out to be about size 34) will fall off my waist.
Measure your own waist and pants, see what you find!
Sizing is chaos.
However dress pants, sports pants and everything that isn't pants is just as bad as for women.