People who don't have these problems don't understand. But growing up is hard.
I don't really think I was truly "grown up" till I was about 30 years old.
My folks meant well but they allowed me to grow up with very little real responsibility. I spent my first 30 years of my life basically in pursuit of FUN and not much else mattered to me.
I was all about the sex, drugs & rock n' roll.
I eventually learned this for myself, after much heart ache, years and years of substance abuse and the near loss of my marriage to my highschool sweetheart wife.
Only you can make the change. If she loves you, she will allow you the time to change. You need to make sure you understand what exactly she is after. If it's reasonable then you must convince her that you're serious about making changes but make sure she understands that it's not likely to occure overnight.
Just make sure she knows you are trying.
If it's a simple matter of you remembering to do your share of the household chores then what others have said about making a list might help.
A marriage is a partnership though. Does she do HER part?
(BTW, I'm 45 and have been married for 26 years now..)
I could have written that, only I took till 40.