For me, at 47, its been our youngest graduating from HS last summer, being able to feel some empty nesting freedom in the future, and 29 years of marriage to my best friend. Much of the stress of raising teenage daughters is gone, my relationship with my husband is comfortable, deep, and strong, and I've learned to say no to some things.
I also had a hysterectomy, which for me, was a very good surgery-I feel much better and no more period!
I think I'm also discovering what I like, who I am, and becoming more comfortable with all of that.