Aniston, now 45, said she has been in a much better place since hitting the milestone, which is something she credits to her career, friends, and relationship with fiance Justin Theroux, reported Contactmusic.
"I've had more fun post-40 than I can remember. From a work point of view, a physical point of view, a psychotherapeutic point of view," she said.
The actress was previously married to fellow actor Brad Pitt for five years until their separation in 2005.