By age 13 my kids can plan their own parties with very little help from me!
DD1's last party consisted of inviting a few girls to sleep over. While here they ordered pizza delivery, watched movies, and ate junk food. Her 11th birthday party was very similar to that- 12 was her Bat Mitzvah and a huge deal around here.
At least, that's what we'd planned on. Instead she kept changing the dates, never settled on one, and one girl didn't get the notice that the party was cancelled and showed up with a birthday gift anyway. We ended up with her sleeping over as a "birthday playdate" and she never got around to scheduling another party with more friends.