Why do I always think badly about my abilities?

Some people lack self-confidence and always see themselves as less able than others which in reality is not the case

This down to the lack of self esteem and belief in ones self from an early age and that is the job of a parent to install that feature as well as confidence, so as soon as you come across something that you would like to do my thoughts are im to old to young to small not clever enough, to think badly of abilities to me is like have a tattoo from birth and it stays with you, my lack of confidence feeds the thought of thinking badly of my abilities where it reaches the point where i get angry or jus not bother at all.

I can understand how you are feeling. I have felt similar feelings. Sometimes the more we know the more we feel that we do not know. It's easier to make ourselves feel self conscious and less deserving that it is to be proudful of ourselves. I think it's important to recognize why you feel bad about your abilities, and then remind yourself 3 times where your abilities did something good for you or made you proud? Or when you start to think bad try to tell yourself "that is not true" and try to counter the thought with another happy thought you have about yourself.

Would like to emphasize the 'think' part of your question. You aren't bad in your abilities, if anything you're quite capable. It's more about the way you perceive yourself to be bad which a lot of the time stems from low self esteem. Perhaps there's a driving factor or just a momentary doubt in your abilities. Regardless I will tell you now, that you have the ability to achieve whatever you desire. But the first think you must learn to do, is believe in yourself and understand that you are very much capable. Change the perception that you are bad. Rather than focusing on a potential negative ability, focus on the positive. Trying in itself shows you have ability. Wishing you all the best