Hi Brookipoo, welcome to the community.
Males will generally begin to show colors after 2-3 months of age.
If you can post a pic it would make it so much easier.
But, for males they generally will be more colorful and will be chasing the females
Some females have little color but possibly have a few spots or yellow green on the tail.
You can see in the picture the more colorful Guppy has a black spot on the lower abdomen but it a spot of color on the outside of the fish's body.
The lower Guppy has a dark spot inside her body near her anal vent. That is called the gravid spot. guppies give live birth, so as the females get close to the due date you can sometimes see the little ones in the female.
They can get pregnant from a very young age (you will be able to see the gravid spot darkening). The females will store sperm and may give birth without a male even up to 6 MONTHS later!!!
There is a good article in my signature, linked for helping out in new tanks which might be of use for your new fish!
Sometimes a female will have a colorful tail.
And you can look for the gonopodium for a male. It is in the anal fins and is very straight and more narrow than the other fins next to it. Checking out a pic of it makes it easier to identify when checking your fish.