In regards to your rattlesnake it has been document that they like some other species of snakes have been known to retain sperm. A very interesting adaption to continue to produce offspring even if you can't find a mate. To the best of my knowlwedge this has never been documented in gila monsters.
Back to your gilas have you had them for 25 years or have you verified that they have been in captivity for 25 years. If you acquired them as adults and have had them for 25 years then who knows what their actual age is.