How can I act more mature?

Okay, so I'm 16 and I don't think I act my age. I'm very lazy, don't do the dishes, laundry, etc. without being asked, and even then I won't do them. I have to be reminded to say thank you, feed the dog, etc. WHen my room is overly messy I will wait until I have to, like having friends over. I will only do chores and such when I'm getting something out of it. and I do more immature things too. Like sometimes I like to talk like a baby wih my sister, and shes in middle school. I do my homework and get decent grades, but thats not good enough for me. I want to do better, I have a lot of problems I want to fix. Any ideas?