Popping or to evert the hemipene is done with all age groups and sizes. Some species are much easier then others. Like rattlesnakes, they evert for you hahahahahahahahaha they are proud.
The reality is, popping or to evert, only tells you the snake IS a male, it does not tell you its a female. If it does not evert, it still could be a male that failed to evert.
Probing is a much more accurate method.
If your really interested in what gender the snakes are, then learn both and use both.
Females also have telltail signs, the little red dots on both sides of the vent are an example.
Last weekend I sexed a friends baby kings at a reptile show. Out of 30 or so, I could sex all but three with visual examination. I could pop all but three as well. That last three, I then probed and they were 2.1.
Many snakes can be sexed mid body and from ten feet away. Its funny but its like with people, some are easy to tell, a few are not.
To learn to do that, you must start somewhere and popping and probing is where you start. Both not one or the other.
After decades working with reptiles, I have learned one thing, do not trust other keepers, hahaqhahahahaahaha.
No offense, but even the big names breeders make lots of mistakes. hahahahahahaha its true. Heck, the last three pairs I recieved from one BIG name breeder, were pairs of males. Good luck