About my teens - first kisses. Other than that I don't want to be a teenager again.
About my 20's - my breasts. I used to have a nice set, weigh gain and 9 years of nursing babies took care of that though.
About my 30's - my activities. When the older kids were younger I did PTA, scouts and the like. It made for a varied social life. I'm still learning to replace all of that now that my youngest has started moving into puberty.
All in all I would have to say that I like who I am now as I start my 40's. I think growing to like myself and have confidence in myself is what helped me to finally get started working on the outside. 40 years gone - hopefully 40+ left to enjoy.