Las Vegas is looking back to the not-so-distant past this weekend. On Oct. 18-19, the annual When We Were Young Festival returns to Sin City for the fourth consecutive year and is once again bringing a cavalcade of throwback ’00s acts to entertain punk, emo, screamo and indie rock fanatics. Just a few of the biggest artists on the bill include chart-toppers Panic! At The Disco (delivering 2005’s “A Fever You Can’t Sweat Out” in its entirety after unofficially retiring in 2023), household name