Is it normal to have a 4 inch erect penis at the age of 19?

I always thought my penis was somewhat abnormal from childhood. I came to know by my parents that at the age of five i had a surgery on it due to problems in passing urine properly. It grew but i think it's too small to satisfy a woman although i masturbate regularly and have erections but it grows to 4 - 4.5 inch max when erect... One day accidentally i saw my father's after he bathed and it was 4 inch flaccid and a lot fatter...Although i am 6 feet tall and hace six packs but still i feel insufficient..