Gap boy 12 slim jeans vguc

This listing is for 12 slim Gap jean joggers. This was worn approx. 3x & is in vguc. My 12 year old outgrew this weight-wise. He says it is too tight & he is 85lbs. On Gap's website the generic sizing chart shows an XL which is a 12 is supposed to be between 75-86lbs. My 12-year old likes things tight so these really do run slim. I'm switching him to "regular" sizing now. There is spot on the back right bottom of the jeans & I am unsure if it is *supposed to* have a bit of coloring to it or if it is some light stain from my son. I really don't know. These are the slim joggers & do have a distressed look. I can take measurements if needed. Also, I have few repeated photos but I think I can live with that w/o obsessing and needlessly retaking photos. The slims are always out of stock which was always a big PITA.