Rachel has the most birthdays shown overall in the seasons.
Phoebe, Joey, Chandler, Ross, Monica and Rachel is the order the group is in age (from oldest to youngest).
According to this episode the oldest of the group is Phoebe (after learning she is a year older than she thought) and the youngest is Rachel. Additionally, it is revealed that Joey is older than Chandler.
Jennifer Aniston wears hair extenstions for the birthday flashbacks.
At the airing of this episode the ages of the main characters was:
- Jennifer Aniston: 31
- Courtney Cox: 36
- Lisa Kudrow: 37
- Matt LeBlanc: 33
- Matthew Perry: 31
- David Schwimmer: 34