at 8 months they are not sexually mature yet, so i wouldn't hold out for a acurate prediction yet, im guessing at around 8 months your looking at still about 9-10 grams, give it till about a year and a half, thats when they usually become sexually mature, but lie danielle said, you may get an accurate answer before, depending on weight,
You should get a sexing loupe from Pangea. It has 30X magnification and an LED. It makes it very easy to see if the pores are present on a 10 gram Crested. If you breed them, this will come in handy instead of having to wait for them to grow.
honestly sexing can happen at 8 months, it all depends on the weight. These guys can vary in weight so much depending on the age that someone with a 4 month old gecko could have one weighing 2g more the someone else simply by the diet.
Normally by 5g males tend to start to show pores. But there are instances where it can take upwards to 12g+ for a male to show pores (had this happen to me, 10g no pores, 12g poof there were pores!), but most common they are pretty easy to see with a loupe at 5-8g. But because of this, some males taking longer to show pores, you will almost never see a breeder selling a for sure female at 10g, they are normally marked as possible or probable females. Normally breeders wait until the 15-18g mark before declaring the gecko is infact female.
So if your female is 8g+ you have a possible female, but dont have your heart set on it..lol
I'm not sure how to tell its weight right now. He/she is kind of nippy. I don't think its scared of us, but it acts like it thinks we're food. So working on that. Its body not including the tail is around 3.5-4 inches long. I'm not a breeder, so I don't have a male or female preference, just thought I'd see for curiosity's sake.
I'll keep an eye on it to see if anything develops as it grows. Thanks for your input, it is much appreciated.