So far the question was not found by me in the archive.
Traditionally Birthday wasn’t celebrated.
Isn’t partying birthday only hedonistic?
You are right. Some of the practices done at birthday parties are hedonistic see http://dinonline.org/2017/10/01/blowing-out-candles-on-a-birthday-cake/ . However celebrating a person’s birthday, is a matter of controversy. There were gedolim who did celebrate their birthdays, and other that didn’t. ( See sources) However to eat a meal as a sign of thanks to H-shem for giving him life, is a good thing, especially when the person reaches 60 or 70, (which shows that the person was not chayiv karet).This should be done in private without making a big fanfare about it. Aside from this it is a day to thank H-shem for giving us life, a day to give tzedakah, etc. Another point regarding a person’s birthday is that the person’s mazal is strong on that day.
Metzudas David Hoshia 7-5, Midrash Sechel Tov Vayeshev 40-20, Ish Chai Re’a 9, 17. Shut Ksav Sofer Y:D 148, Levush Yosef pg.353, Sefer Hazikaromn Zichron Shomo pg. 190-220, Ohr Yisroel 24 pg. 175-196. Halachically Speaking 9-11.