The biggest problem is the lack of partner with knowledge of satisfying pleasures fit to old lizards. Some of these activities might include oral stimulation so if the female partner of the lizard knows how to get the lizard "interested" then the quality of pleasure that old lizard will have will be absolutely phenomenal despite of lizard's age!
Now when referring to humans, my "fan" that is older say about me that older people like him can have quality sexual experiences if they get the right female partner (like me)!