Is it possible to do a complete overhaul of your personality?

I've heard that your personality is pretty much set in stone during the early years of life... I've noticed that I have a neurotic personality. I've pushed a lot of people away because of this and I hate myself for it. I have no friends and a lot of people think bad of me. I'm 20 years old and I am wondering if it's too late for me in regards to personality overhaul.