I think my son's last year was 12 or 13...yeah - 13. He went out with a bunch of friends. When he was 14, one of his friends had a big Halloween party, and he decided to go to that, instead of ToT. He hasn't ToT'd since.
DS1 is hugely into Halloween and costumes. He made his own Eric Draven costume in 9th grade, his own Joker costume (based on Heath Ledger - we bought most of it in thrift stores and did a lot of dying things purple) in 10th grade, and his own Rorschach costume last year. This year is his masterpiece. He's being Captain Jack Sparrow, and has poured a ton of money and online research into components. He's playing with makeup and has to find a hat...and does a pretty good imitation of Capt. Jack, to boot. I think he's going to be awesome...a nice Halloween "grand finale" for high school.
ETA: My last year of ToT was when I was either 15 or 16. I didn't want to give up on it.