The Palms are slow to mature. You can compare the thickness of the legs, the hens will have narrower legs. Also the toms will have less feathers on the head.
The best way is to vent sex them which once you know what you are looking for is close to 100% accurate. You need to be very gentle and careful as it's easy to injure the bird.
I'm right handed so this is how I do it. Hold the bird with my right arm against my side, head under my elbow. with the right hand lift the tail feathers and using thumb and forfinger gently lift the top of the vent towards the tail. (you may get poo'd on at this point- it's just the turkey saying thank you for probing me)
With your left hand, I use thumb and forfinger again. VERY GENTLY pull the bottom of the vent down. On the toms you will see 2 small round balls, these are the sperm ducts on the hens you will see 2 flaps of skin.
If you have a couple to compare it's real easy to see the difference from male to female.
Like I said before go real easy as you can injure the bird.
Steve in NC