Yes, your gecko is old enough to eat giant mealworms - head and everything. However, giant mealworms are made for the fishing industry, not for pet food. They're feed chemicals that prevent them from leaving the larval stage. It's not proven one way or the other that these chemicals are harmful to the geckos, but I wouldn't care to risk that they are. You can safely feed many regular sized mealworms, or use superworms instead.
There is a type of "Large" Mealworm that is Naturally Occuring.. They do sometime go by the name of Giant Mealworms.. Or King Mealworms. Their Scientific name is Zophobas artratus. If you google the scientific name you will see a mealworm that looks a lot different than the common Tenebrio molitor. There was a little bit of confusion on this same matter in this thread [link]. The Zophobas are perfectly healthy to feed. One big difference between these two is that the Zophobas cannot be refrigerated. They must be kept at room temperature. The Zophobas also move around a lot more than the Tenebrios. :main_thumbsup:
I've seen the Zophobas before and used them myself a few times. I've never seen them sold at a shop or commercial store though. They usually sell giants that can be refrigerated.
Giant Mealworms havent been proven harmfull for your reptiles, but they HAVE been proven less nutricious by several places that sell them. Stick with the largest natural mealies you can find or upgrade to Superworms.
If you want your meal worms active, invest in a fresh pineapple (to feed them.
Works wonders and great on upping their size too ....my gecks used to try to hold out till the wax worms were given. Not any more since I grabbed onto feeding the pineapple. I use feeding bowls in the habitats and find both meal and waxes clinging to the small piece I include in their bowl. Take care.