Don't sweat the small stuff

"Don't sweat the small stuff," they say. Yeah, like I can really do that! I worry. I fret. I stress. I panic. All of these things happen to people like me, people who are people-pleasing, perfectionist, low self-esteem types. I keep telling myself I'm gonna stop being this way. I'm gonna get over this incessant need to please the world. I'm gonna get myself a backbone and just a tiny air of self-confidence (Not too much though). I'm gonna learn the word "no" and actually use it from time to time. I'm gonna do my best on a project and then leave it alone rather than stress out over it until I'm nearly sick. I'm wondering... Is it possible, at the age of 42, to change part of what makes you who you are?