I'm still fairly new myself. This forum,along with a couple books have been very helpful in learning more about cornsnakes & caring for them.
Some books to check out:
Corn Snakes In Captivity-by Don Soderberg (I picked up a used one on Amazon, that ended up an autographed copy, for pretty cheap).
Corn snakes; The Comprehensive Owner's Guide-by Kathy Love & Bill Love
Another very helpful book is Cornsnake Morph Guide
Your snake is likely less than a year old. I have hatchlings that are 11", & they're 4 weeks old.
I don't know how old is "too old" to pop the babies, for sexing.
A good thing to have on hand is a digital scale. You can pick one up at Walmart for $20-$35, depending on which one you get. I got the one that goes up to 11lbs, for $35.
It's a good idea to track the weight of your snake.
There's a lot of knowledge on this forum, & you will pick up alot from the people here.