No, they all grow at different rates. It's all estimates if you don't know the day they hatched.
You should keep records of your little guy. Just measure the length and weigh him once a month. The weight is a good indication that he is eating and healthy. For example, if yours is losing weight month after month then there could be a health issue. It could even be something basic like your temperatures are too low so his appetite is down. You may detect this with keeping records before it gets into a serious health issues. I don't bother with weekly records because on a weekly basis I noticed weights can go up and down slightly, but over a longer period(like a month) it should go up.
