could someone tell me how big/long a year old blood should be because my male sumatran black blood and my female sumatran red are both just about a year old (about 9 0r 10 months). and they are only about 20 inches long! they are nice and thick, their weight is good and i know bloods are short snakes in the first place but mine seem too short for a year old. is 18-20 inches normal for a year old blood?