That sounds big to me too. Just did a weight on a few of mine out of curiosity and my 10 month old is 162g and if he's 20in I'd be surprised. He also just ate a hopper so he's probably a little lighter than the 162g. Granted I feed less but still a major difference in size! My guy eats a hopper every two weeks.

My hypo and sunglow that are around a year and 8 months are around 3ft or less and 3.5ft. My hypo male being the larger one since he won't stop growing no matter how little he is fed. The hypo male is 626g after just eating and the sunglow female is 484g after just eating. The male hypo just got moved to weaned-small rats every 3 weeks and the sunglow just had her first rat but she will be getting an adult mouse the next few meals again. I can't tell either one ate a rat but I still think the rat is a little much for my sunglow right now.